+This is equivalent to the following, where 2863311531 is the multiplicative
+inverse of 3, and 1431655766 is ((2^32)-1)/3+1:
+void bar(unsigned n) {
+ if (n * 2863311531U < 1431655766U)
+ true();
+}
+
+The same transformation can work with an even modulo with the addition of a
+rotate: rotate the result of the multiply to the right by the number of bits
+which need to be zero for the condition to be true, and shrink the compare RHS
+by the same amount. Unless the target supports rotates, though, that
+transformation probably isn't worthwhile.
+
+The transformation can also easily be made to work with non-zero equality
+comparisons: just transform, for example, "n % 3 == 1" to "(n-1) % 3 == 0".
+
+//===---------------------------------------------------------------------===//
+
+Better mod/ref analysis for scanf would allow us to eliminate the vtable and a
+bunch of other stuff from this example (see PR1604):
+
+#include <cstdio>
+struct test {
+ int val;
+ virtual ~test() {}
+};
+
+int main() {
+ test t;
+ std::scanf("%d", &t.val);
+ std::printf("%d\n", t.val);
+}
+
+//===---------------------------------------------------------------------===//
+
+These functions perform the same computation, but produce different assembly.
+
+define i8 @select(i8 %x) readnone nounwind {
+ %A = icmp ult i8 %x, 250
+ %B = select i1 %A, i8 0, i8 1
+ ret i8 %B
+}
+
+define i8 @addshr(i8 %x) readnone nounwind {
+ %A = zext i8 %x to i9
+ %B = add i9 %A, 6 ;; 256 - 250 == 6
+ %C = lshr i9 %B, 8
+ %D = trunc i9 %C to i8
+ ret i8 %D
+}
+
+//===---------------------------------------------------------------------===//
+
+From gcc bug 24696:
+int
+f (unsigned long a, unsigned long b, unsigned long c)
+{
+ return ((a & (c - 1)) != 0) || ((b & (c - 1)) != 0);
+}
+int
+f (unsigned long a, unsigned long b, unsigned long c)
+{
+ return ((a & (c - 1)) != 0) | ((b & (c - 1)) != 0);
+}
+Both should combine to ((a|b) & (c-1)) != 0. Currently not optimized with
+"clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 20192:
+#define PMD_MASK (~((1UL << 23) - 1))
+void clear_pmd_range(unsigned long start, unsigned long end)
+{
+ if (!(start & ~PMD_MASK) && !(end & ~PMD_MASK))
+ f();
+}
+The expression should optimize to something like
+"!((start|end)&~PMD_MASK). Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 3756:
+int
+pn (int n)
+{
+ return (n >= 0 ? 1 : -1);
+}
+Should combine to (n >> 31) | 1. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts | llc".
+
+//===---------------------------------------------------------------------===//
+
+void a(int variable)
+{
+ if (variable == 4 || variable == 6)
+ bar();
+}
+This should optimize to "if ((variable | 2) == 6)". Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts | llc".
+
+//===---------------------------------------------------------------------===//
+
+unsigned int f(unsigned int i, unsigned int n) {++i; if (i == n) ++i; return
+i;}
+unsigned int f2(unsigned int i, unsigned int n) {++i; i += i == n; return i;}
+These should combine to the same thing. Currently, the first function
+produces better code on X86.
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 15784:
+#define abs(x) x>0?x:-x
+int f(int x, int y)
+{
+ return (abs(x)) >= 0;
+}
+This should optimize to x == INT_MIN. (With -fwrapv.) Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 14753:
+void
+rotate_cst (unsigned int a)
+{
+ a = (a << 10) | (a >> 22);
+ if (a == 123)
+ bar ();
+}
+void
+minus_cst (unsigned int a)
+{
+ unsigned int tem;
+
+ tem = 20 - a;
+ if (tem == 5)
+ bar ();
+}
+void
+mask_gt (unsigned int a)
+{
+ /* This is equivalent to a > 15. */
+ if ((a & ~7) > 8)
+ bar ();
+}
+void
+rshift_gt (unsigned int a)
+{
+ /* This is equivalent to a > 23. */
+ if ((a >> 2) > 5)
+ bar ();
+}
+All should simplify to a single comparison. All of these are
+currently not optimized with "clang -emit-llvm-bc | opt
+-std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 32605:
+int c(int* x) {return (char*)x+2 == (char*)x;}
+Should combine to 0. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts" (although llc can optimize it).
+
+//===---------------------------------------------------------------------===//
+
+int a(unsigned b) {return ((b << 31) | (b << 30)) >> 31;}
+Should be combined to "((b >> 1) | b) & 1". Currently not optimized
+with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned x, unsigned y) { return x | (y & 1) | (y & 2);}
+Should combine to "x | (y & 3)". Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (~a & c) | ((c|a) & b);}
+Should fold to "(~a & c) | (a & b)". Currently not optimized with
+"clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a,int b) {return (~(a|b))|a;}
+Should fold to "a|~b". Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b) {return (a&&b) || (a&&!b);}
+Should fold to "a". Currently not optimized with "clang -emit-llvm-bc
+| opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (a&&b) || (!a&&c);}
+Should fold to "a ? b : c", or at least something sane. Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (a&&b) || (a&&c) || (a&&b&&c);}
+Should fold to a && (b || c). Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return x | ((x & 8) ^ 8);}
+Should combine to x | 8. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return x ^ ((x & 8) ^ 8);}
+Should also combine to x | 8. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return (x & 8) == 0 ? -1 : -9;}
+Should combine to (x | -9) ^ 8. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return (x & 8) == 0 ? -9 : -1;}
+Should combine to x | -9. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return ((x | -9) ^ 8) & x;}
+Should combine to x & -9. Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned a) {return a * 0x11111111 >> 28 & 1;}
+Should combine to "a * 0x88888888 >> 31". Currently not optimized
+with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(char* x) {if ((*x & 32) == 0) return b();}
+There's an unnecessary zext in the generated code with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned long long x) {return 40 * (x >> 1);}
+Should combine to "20 * (((unsigned)x) & -2)". Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+This was noticed in the entryblock for grokdeclarator in 403.gcc:
+
+ %tmp = icmp eq i32 %decl_context, 4
+ %decl_context_addr.0 = select i1 %tmp, i32 3, i32 %decl_context
+ %tmp1 = icmp eq i32 %decl_context_addr.0, 1
+ %decl_context_addr.1 = select i1 %tmp1, i32 0, i32 %decl_context_addr.0
+
+tmp1 should be simplified to something like:
+ (!tmp || decl_context == 1)
+
+This allows recursive simplifications, tmp1 is used all over the place in
+the function, e.g. by:
+
+ %tmp23 = icmp eq i32 %decl_context_addr.1, 0 ; <i1> [#uses=1]
+ %tmp24 = xor i1 %tmp1, true ; <i1> [#uses=1]
+ %or.cond8 = and i1 %tmp23, %tmp24 ; <i1> [#uses=1]
+
+later.
+
+//===---------------------------------------------------------------------===//
+
+[STORE SINKING]
+
+Store sinking: This code:
+
+void f (int n, int *cond, int *res) {
+ int i;
+ *res = 0;
+ for (i = 0; i < n; i++)
+ if (*cond)
+ *res ^= 234; /* (*) */
+}
+
+On this function GVN hoists the fully redundant value of *res, but nothing
+moves the store out. This gives us this code:
+
+bb: ; preds = %bb2, %entry
+ %.rle = phi i32 [ 0, %entry ], [ %.rle6, %bb2 ]
+ %i.05 = phi i32 [ 0, %entry ], [ %indvar.next, %bb2 ]
+ %1 = load i32* %cond, align 4
+ %2 = icmp eq i32 %1, 0
+ br i1 %2, label %bb2, label %bb1
+
+bb1: ; preds = %bb
+ %3 = xor i32 %.rle, 234
+ store i32 %3, i32* %res, align 4
+ br label %bb2
+
+bb2: ; preds = %bb, %bb1
+ %.rle6 = phi i32 [ %3, %bb1 ], [ %.rle, %bb ]
+ %indvar.next = add i32 %i.05, 1
+ %exitcond = icmp eq i32 %indvar.next, %n
+ br i1 %exitcond, label %return, label %bb
+
+DSE should sink partially dead stores to get the store out of the loop.
+
+Here's another partial dead case:
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12395
+
+//===---------------------------------------------------------------------===//
+
+Scalar PRE hoists the mul in the common block up to the else:
+
+int test (int a, int b, int c, int g) {
+ int d, e;
+ if (a)
+ d = b * c;
+ else
+ d = b - c;
+ e = b * c + g;
+ return d + e;
+}
+
+It would be better to do the mul once to reduce codesize above the if.
+This is GCC PR38204.
+
+//===---------------------------------------------------------------------===//
+
+[STORE SINKING]
+
+GCC PR37810 is an interesting case where we should sink load/store reload
+into the if block and outside the loop, so we don't reload/store it on the
+non-call path.
+
+for () {
+ *P += 1;
+ if ()
+ call();
+ else
+ ...
+->
+tmp = *P
+for () {
+ tmp += 1;
+ if () {
+ *P = tmp;
+ call();
+ tmp = *P;
+ } else ...
+}
+*P = tmp;
+
+We now hoist the reload after the call (Transforms/GVN/lpre-call-wrap.ll), but
+we don't sink the store. We need partially dead store sinking.
+
+//===---------------------------------------------------------------------===//
+
+[LOAD PRE CRIT EDGE SPLITTING]
+
+GCC PR37166: Sinking of loads prevents SROA'ing the "g" struct on the stack
+leading to excess stack traffic. This could be handled by GVN with some crazy
+symbolic phi translation. The code we get looks like (g is on the stack):
+
+bb2: ; preds = %bb1
+..
+ %9 = getelementptr %struct.f* %g, i32 0, i32 0
+ store i32 %8, i32* %9, align bel %bb3
+
+bb3: ; preds = %bb1, %bb2, %bb
+ %c_addr.0 = phi %struct.f* [ %g, %bb2 ], [ %c, %bb ], [ %c, %bb1 ]
+ %b_addr.0 = phi %struct.f* [ %b, %bb2 ], [ %g, %bb ], [ %b, %bb1 ]
+ %10 = getelementptr %struct.f* %c_addr.0, i32 0, i32 0
+ %11 = load i32* %10, align 4
+
+%11 is partially redundant, an in BB2 it should have the value %8.
+
+GCC PR33344 and PR35287 are similar cases.
+
+
+//===---------------------------------------------------------------------===//
+
+[LOAD PRE]
+
+There are many load PRE testcases in testsuite/gcc.dg/tree-ssa/loadpre* in the
+GCC testsuite, ones we don't get yet are (checked through loadpre25):
+
+[CRIT EDGE BREAKING]
+loadpre3.c predcom-4.c
+
+[PRE OF READONLY CALL]
+loadpre5.c
+
+[TURN SELECT INTO BRANCH]
+loadpre14.c loadpre15.c
+
+actually a conditional increment: loadpre18.c loadpre19.c
+
+
+//===---------------------------------------------------------------------===//
+
+[SCALAR PRE]
+There are many PRE testcases in testsuite/gcc.dg/tree-ssa/ssa-pre-*.c in the
+GCC testsuite.
+
+//===---------------------------------------------------------------------===//
+
+There are some interesting cases in testsuite/gcc.dg/tree-ssa/pred-comm* in the
+GCC testsuite. For example, we get the first example in predcom-1.c, but
+miss the second one:
+
+unsigned fib[1000];
+unsigned avg[1000];
+
+__attribute__ ((noinline))
+void count_averages(int n) {
+ int i;
+ for (i = 1; i < n; i++)
+ avg[i] = (((unsigned long) fib[i - 1] + fib[i] + fib[i + 1]) / 3) & 0xffff;
+}
+
+which compiles into two loads instead of one in the loop.
+
+predcom-2.c is the same as predcom-1.c
+
+predcom-3.c is very similar but needs loads feeding each other instead of
+store->load.
+
+
+//===---------------------------------------------------------------------===//
+
+Type based alias analysis:
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705
+
+//===---------------------------------------------------------------------===//
+
+A/B get pinned to the stack because we turn an if/then into a select instead
+of PRE'ing the load/store. This may be fixable in instcombine:
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37892
+
+struct X { int i; };
+int foo (int x) {
+ struct X a;
+ struct X b;
+ struct X *p;
+ a.i = 1;
+ b.i = 2;
+ if (x)
+ p = &a;
+ else
+ p = &b;
+ return p->i;
+}
+
+//===---------------------------------------------------------------------===//
+
+Interesting missed case because of control flow flattening (should be 2 loads):
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26629
+With: llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as |
+ opt -mem2reg -gvn -instcombine | llvm-dis
+we miss it because we need 1) CRIT EDGE 2) MULTIPLE DIFFERENT
+VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
+
+//===---------------------------------------------------------------------===//
+
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19633
+We could eliminate the branch condition here, loading from null is undefined:
+
+struct S { int w, x, y, z; };
+struct T { int r; struct S s; };
+void bar (struct S, int);
+void foo (int a, struct T b)
+{
+ struct S *c = 0;
+ if (a)
+ c = &b.s;
+ bar (*c, a);
+}
+
+//===---------------------------------------------------------------------===//
+
+simplifylibcalls should do several optimizations for strspn/strcspn:
+
+strcspn(x, "") -> strlen(x)
+strcspn("", x) -> 0
+strspn("", x) -> 0
+strspn(x, "") -> strlen(x)
+strspn(x, "a") -> strchr(x, 'a')-x
+
+strcspn(x, "a") -> inlined loop for up to 3 letters (similarly for strspn):
+
+size_t __strcspn_c3 (__const char *__s, int __reject1, int __reject2,
+ int __reject3) {
+ register size_t __result = 0;
+ while (__s[__result] != '\0' && __s[__result] != __reject1 &&
+ __s[__result] != __reject2 && __s[__result] != __reject3)
+ ++__result;
+ return __result;
+}
+
+This should turn into a switch on the character. See PR3253 for some notes on
+codegen.
+
+456.hmmer apparently uses strcspn and strspn a lot. 471.omnetpp uses strspn.
+
+//===---------------------------------------------------------------------===//
+
+"gas" uses this idiom:
+ else if (strchr ("+-/*%|&^:[]()~", *intel_parser.op_string))
+..
+ else if (strchr ("<>", *intel_parser.op_string)
+
+Those should be turned into a switch.
+
+//===---------------------------------------------------------------------===//
+
+252.eon contains this interesting code:
+
+ %3072 = getelementptr [100 x i8]* %tempString, i32 0, i32 0
+ %3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
+ %strlen = call i32 @strlen(i8* %3072) ; uses = 1
+ %endptr = getelementptr [100 x i8]* %tempString, i32 0, i32 %strlen
+ call void @llvm.memcpy.i32(i8* %endptr,
+ i8* getelementptr ([5 x i8]* @"\01LC42", i32 0, i32 0), i32 5, i32 1)
+ %3074 = call i32 @strlen(i8* %endptr) nounwind readonly
+
+This is interesting for a couple reasons. First, in this:
+
+ %3073 = call i8* @strcpy(i8* %3072, i8* %3071) nounwind
+ %strlen = call i32 @strlen(i8* %3072)
+
+The strlen could be replaced with: %strlen = sub %3072, %3073, because the
+strcpy call returns a pointer to the end of the string. Based on that, the
+endptr GEP just becomes equal to 3073, which eliminates a strlen call and GEP.
+
+Second, the memcpy+strlen strlen can be replaced with:
+
+ %3074 = call i32 @strlen([5 x i8]* @"\01LC42") nounwind readonly
+
+Because the destination was just copied into the specified memory buffer. This,
+in turn, can be constant folded to "4".
+
+In other code, it contains:
+
+ %endptr6978 = bitcast i8* %endptr69 to i32*
+ store i32 7107374, i32* %endptr6978, align 1
+ %3167 = call i32 @strlen(i8* %endptr69) nounwind readonly
+
+Which could also be constant folded. Whatever is producing this should probably
+be fixed to leave this as a memcpy from a string.
+
+Further, eon also has an interesting partially redundant strlen call:
+
+bb8: ; preds = %_ZN18eonImageCalculatorC1Ev.exit
+ %682 = getelementptr i8** %argv, i32 6 ; <i8**> [#uses=2]
+ %683 = load i8** %682, align 4 ; <i8*> [#uses=4]
+ %684 = load i8* %683, align 1 ; <i8> [#uses=1]
+ %685 = icmp eq i8 %684, 0 ; <i1> [#uses=1]
+ br i1 %685, label %bb10, label %bb9
+
+bb9: ; preds = %bb8
+ %686 = call i32 @strlen(i8* %683) nounwind readonly
+ %687 = icmp ugt i32 %686, 254 ; <i1> [#uses=1]
+ br i1 %687, label %bb10, label %bb11
+
+bb10: ; preds = %bb9, %bb8
+ %688 = call i32 @strlen(i8* %683) nounwind readonly
+
+This could be eliminated by doing the strlen once in bb8, saving code size and
+improving perf on the bb8->9->10 path.
+
+//===---------------------------------------------------------------------===//
+
+I see an interesting fully redundant call to strlen left in 186.crafty:InputMove
+which looks like:
+ %movetext11 = getelementptr [128 x i8]* %movetext, i32 0, i32 0
+
+
+bb62: ; preds = %bb55, %bb53
+ %promote.0 = phi i32 [ %169, %bb55 ], [ 0, %bb53 ]
+ %171 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
+ %172 = add i32 %171, -1 ; <i32> [#uses=1]
+ %173 = getelementptr [128 x i8]* %movetext, i32 0, i32 %172
+
+... no stores ...
+ br i1 %or.cond, label %bb65, label %bb72
+
+bb65: ; preds = %bb62
+ store i8 0, i8* %173, align 1
+ br label %bb72
+
+bb72: ; preds = %bb65, %bb62
+ %trank.1 = phi i32 [ %176, %bb65 ], [ -1, %bb62 ]
+ %177 = call i32 @strlen(i8* %movetext11) nounwind readonly align 1
+
+Note that on the bb62->bb72 path, that the %177 strlen call is partially
+redundant with the %171 call. At worst, we could shove the %177 strlen call
+up into the bb65 block moving it out of the bb62->bb72 path. However, note
+that bb65 stores to the string, zeroing out the last byte. This means that on
+that path the value of %177 is actually just %171-1. A sub is cheaper than a
+strlen!
+
+This pattern repeats several times, basically doing:
+
+ A = strlen(P);
+ P[A-1] = 0;
+ B = strlen(P);
+ where it is "obvious" that B = A-1.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty contains this interesting pattern:
+
+%77 = call i8* @strstr(i8* getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0),
+ i8* %30)
+%phitmp648 = icmp eq i8* %77, getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0)
+br i1 %phitmp648, label %bb70, label %bb76
+
+bb70: ; preds = %OptionMatch.exit91, %bb69
+ %78 = call i32 @strlen(i8* %30) nounwind readonly align 1 ; <i32> [#uses=1]
+
+This is basically:
+ cststr = "abcdef";
+ if (strstr(cststr, P) == cststr) {
+ x = strlen(P);
+ ...
+
+The strstr call would be significantly cheaper written as:
+
+cststr = "abcdef";
+if (memcmp(P, str, strlen(P)))
+ x = strlen(P);
+
+This is memcmp+strlen instead of strstr. This also makes the strlen fully
+redundant.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty also contains this code:
+
+%1906 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
+%1907 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1906
+%1908 = call i8* @strcpy(i8* %1907, i8* %1905) nounwind align 1
+%1909 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
+%1910 = getelementptr [32 x i8]* @pgn_event, i32 0, i32 %1909
+
+The last strlen is computable as 1908-@pgn_event, which means 1910=1908.
+
+//===---------------------------------------------------------------------===//
+
+186.crafty has this interesting pattern with the "out.4543" variable:
+
+call void @llvm.memcpy.i32(
+ i8* getelementptr ([10 x i8]* @out.4543, i32 0, i32 0),
+ i8* getelementptr ([7 x i8]* @"\01LC28700", i32 0, i32 0), i32 7, i32 1)
+%101 = call@printf(i8* ... @out.4543, i32 0, i32 0)) nounwind
+
+It is basically doing:
+
+ memcpy(globalarray, "string");
+ printf(..., globalarray);
+
+Anyway, by knowing that printf just reads the memory and forward substituting
+the string directly into the printf, this eliminates reads from globalarray.
+Since this pattern occurs frequently in crafty (due to the "DisplayTime" and
+other similar functions) there are many stores to "out". Once all the printfs
+stop using "out", all that is left is the memcpy's into it. This should allow
+globalopt to remove the "stored only" global.
+
+//===---------------------------------------------------------------------===//
+
+This code:
+
+define inreg i32 @foo(i8* inreg %p) nounwind {
+ %tmp0 = load i8* %p
+ %tmp1 = ashr i8 %tmp0, 5
+ %tmp2 = sext i8 %tmp1 to i32
+ ret i32 %tmp2
+}
+
+could be dagcombine'd to a sign-extending load with a shift.
+For example, on x86 this currently gets this:
+
+ movb (%eax), %al
+ sarb $5, %al
+ movsbl %al, %eax
+
+while it could get this:
+
+ movsbl (%eax), %eax
+ sarl $5, %eax
+
+//===---------------------------------------------------------------------===//
+
+GCC PR31029:
+
+int test(int x) { return 1-x == x; } // --> return false
+int test2(int x) { return 2-x == x; } // --> return x == 1 ?
+
+Always foldable for odd constants, what is the rule for even?
+
+//===---------------------------------------------------------------------===//
+
+PR 3381: GEP to field of size 0 inside a struct could be turned into GEP
+for next field in struct (which is at same address).
+
+For example: store of float into { {{}}, float } could be turned into a store to
+the float directly.
+
+//===---------------------------------------------------------------------===//
+
+#include <math.h>
+double foo(double a) { return sin(a); }
+
+This compiles into this on x86-64 Linux:
+foo:
+ subq $8, %rsp
+ call sin
+ addq $8, %rsp
+ ret
+vs:
+
+foo:
+ jmp sin
+
+//===---------------------------------------------------------------------===//
+
+The arg promotion pass should make use of nocapture to make its alias analysis
+stuff much more precise.
+
+//===---------------------------------------------------------------------===//
+
+The following functions should be optimized to use a select instead of a
+branch (from gcc PR40072):
+
+char char_int(int m) {if(m>7) return 0; return m;}
+int int_char(char m) {if(m>7) return 0; return m;}
+
+//===---------------------------------------------------------------------===//
+
+int func(int a, int b) { if (a & 0x80) b |= 0x80; else b &= ~0x80; return b; }
+
+Generates this:
+
+define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
+entry:
+ %0 = and i32 %a, 128 ; <i32> [#uses=1]
+ %1 = icmp eq i32 %0, 0 ; <i1> [#uses=1]
+ %2 = or i32 %b, 128 ; <i32> [#uses=1]
+ %3 = and i32 %b, -129 ; <i32> [#uses=1]
+ %b_addr.0 = select i1 %1, i32 %3, i32 %2 ; <i32> [#uses=1]
+ ret i32 %b_addr.0
+}
+
+However, it's functionally equivalent to:
+
+ b = (b & ~0x80) | (a & 0x80);
+
+Which generates this:
+
+define i32 @func(i32 %a, i32 %b) nounwind readnone ssp {
+entry:
+ %0 = and i32 %b, -129 ; <i32> [#uses=1]
+ %1 = and i32 %a, 128 ; <i32> [#uses=1]
+ %2 = or i32 %0, %1 ; <i32> [#uses=1]
+ ret i32 %2
+}
+
+This can be generalized for other forms:
+
+ b = (b & ~0x80) | (a & 0x40) << 1;
+
+//===---------------------------------------------------------------------===//
+
+These two functions produce different code. They shouldn't:
+
+#include <stdint.h>
+
+uint8_t p1(uint8_t b, uint8_t a) {
+ b = (b & ~0xc0) | (a & 0xc0);
+ return (b);
+}
+
+uint8_t p2(uint8_t b, uint8_t a) {
+ b = (b & ~0x40) | (a & 0x40);
+ b = (b & ~0x80) | (a & 0x80);
+ return (b);
+}
+
+define zeroext i8 @p1(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
+entry:
+ %0 = and i8 %b, 63 ; <i8> [#uses=1]
+ %1 = and i8 %a, -64 ; <i8> [#uses=1]
+ %2 = or i8 %1, %0 ; <i8> [#uses=1]
+ ret i8 %2
+}
+
+define zeroext i8 @p2(i8 zeroext %b, i8 zeroext %a) nounwind readnone ssp {
+entry:
+ %0 = and i8 %b, 63 ; <i8> [#uses=1]
+ %.masked = and i8 %a, 64 ; <i8> [#uses=1]
+ %1 = and i8 %a, -128 ; <i8> [#uses=1]
+ %2 = or i8 %1, %0 ; <i8> [#uses=1]
+ %3 = or i8 %2, %.masked ; <i8> [#uses=1]
+ ret i8 %3
+}
+
+//===---------------------------------------------------------------------===//
+
+IPSCCP does not currently propagate argument dependent constants through
+functions where it does not not all of the callers. This includes functions
+with normal external linkage as well as templates, C99 inline functions etc.
+Specifically, it does nothing to:
+
+define i32 @test(i32 %x, i32 %y, i32 %z) nounwind {
+entry:
+ %0 = add nsw i32 %y, %z
+ %1 = mul i32 %0, %x
+ %2 = mul i32 %y, %z
+ %3 = add nsw i32 %1, %2
+ ret i32 %3
+}
+
+define i32 @test2() nounwind {
+entry:
+ %0 = call i32 @test(i32 1, i32 2, i32 4) nounwind
+ ret i32 %0
+}
+
+It would be interesting extend IPSCCP to be able to handle simple cases like
+this, where all of the arguments to a call are constant. Because IPSCCP runs
+before inlining, trivial templates and inline functions are not yet inlined.
+The results for a function + set of constant arguments should be memoized in a
+map.
+
+//===---------------------------------------------------------------------===//
+
+The libcall constant folding stuff should be moved out of SimplifyLibcalls into
+libanalysis' constantfolding logic. This would allow IPSCCP to be able to
+handle simple things like this:
+
+static int foo(const char *X) { return strlen(X); }
+int bar() { return foo("abcd"); }
+
+//===---------------------------------------------------------------------===//
+
+InstCombine should use SimplifyDemandedBits to remove the or instruction:
+
+define i1 @test(i8 %x, i8 %y) {
+ %A = or i8 %x, 1
+ %B = icmp ugt i8 %A, 3
+ ret i1 %B
+}
+
+Currently instcombine calls SimplifyDemandedBits with either all bits or just
+the sign bit, if the comparison is obviously a sign test. In this case, we only
+need all but the bottom two bits from %A, and if we gave that mask to SDB it
+would delete the or instruction for us.
+
+//===---------------------------------------------------------------------===//
+
+functionattrs doesn't know much about memcpy/memset. This function should be
+marked readnone rather than readonly, since it only twiddles local memory, but
+functionattrs doesn't handle memset/memcpy/memmove aggressively:
+
+struct X { int *p; int *q; };
+int foo() {
+ int i = 0, j = 1;
+ struct X x, y;
+ int **p;
+ y.p = &i;
+ x.q = &j;
+ p = __builtin_memcpy (&x, &y, sizeof (int *));
+ return **p;
+}
projects / oota-llvm.git / blobdiff