Implement rdar://7860110 (also in target/readme.txt) narrowing

[oota-llvm.git] / lib / Target / README.txt

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index ce84cbb79d7b90e053b84da0688fcffe99e446d5..150143bec7f69105eb4dac664675dee36a96fa63 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -263,19 +263,6 @@ if anyone cared enough about sincos.
 
 //===---------------------------------------------------------------------===//
 
-Turn this into a single byte store with no load (the other 3 bytes are
-unmodified):
-
-define void @test(i32* %P) {
-       %tmp = load i32* %P
-        %tmp14 = or i32 %tmp, 3305111552
-        %tmp15 = and i32 %tmp14, 3321888767
-        store i32 %tmp15, i32* %P
-        ret void
-}
-
-//===---------------------------------------------------------------------===//
-
 quantum_sigma_x in 462.libquantum contains the following loop:
 
       for(i=0; i<reg->size; i++)
@@ -1751,12 +1738,95 @@ from gcc.
 Missed instcombine transformation:
 define i32 @a(i32 %x) nounwind readnone {
 entry:
-  %shr = lshr i32 %x, 5                           ; <i32> [#uses=1]
-  %xor = xor i32 %shr, 67108864                   ; <i32> [#uses=1]
-  %sub = add i32 %xor, -67108864                  ; <i32> [#uses=1]
+  %rem = srem i32 %x, 32
+  %shl = shl i32 1, %rem
+  ret i32 %shl
+}
+
+The srem can be transformed to an and because if x is negative, the shift is
+undefined. Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+Missed instcombine/dagcombine transformation:
+define i32 @a(i32 %x, i32 %y) nounwind readnone {
+entry:
+  %mul = mul i32 %y, -8
+  %sub = sub i32 %x, %mul
   ret i32 %sub
 }
 
-This function is equivalent to "ashr i32 %x, 5".  Testcase derived from gcc.
+Should compile to something like x+y*8, but currently compiles to an
+inefficient result.  Testcase derived from gcc.
 
 //===---------------------------------------------------------------------===//
+
+Missed instcombine/dagcombine transformation:
+define void @lshift_lt(i8 zeroext %a) nounwind {
+entry:
+  %conv = zext i8 %a to i32
+  %shl = shl i32 %conv, 3
+  %cmp = icmp ult i32 %shl, 33
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  tail call void @bar() nounwind
+  ret void
+
+if.end:
+  ret void
+}
+declare void @bar() nounwind
+
+The shift should be eliminated.  Testcase derived from gcc.
+
+//===---------------------------------------------------------------------===//
+
+These compile into different code, one gets recognized as a switch and the
+other doesn't due to phase ordering issues (PR6212):
+
+int test1(int mainType, int subType) {
+  if (mainType == 7)
+    subType = 4;
+  else if (mainType == 9)
+    subType = 6;
+  else if (mainType == 11)
+    subType = 9;
+  return subType;
+}
+
+int test2(int mainType, int subType) {
+  if (mainType == 7)
+    subType = 4;
+  if (mainType == 9)
+    subType = 6;
+  if (mainType == 11)
+    subType = 9;
+  return subType;
+}
+
+//===---------------------------------------------------------------------===//
+
+The following test case (from PR6576):
+
+define i32 @mul(i32 %a, i32 %b) nounwind readnone {
+entry:
+ %cond1 = icmp eq i32 %b, 0                      ; <i1> [#uses=1]
+ br i1 %cond1, label %exit, label %bb.nph
+bb.nph:                                           ; preds = %entry
+ %tmp = mul i32 %b, %a                           ; <i32> [#uses=1]
+ ret i32 %tmp
+exit:                                             ; preds = %entry
+ ret i32 0
+}
+
+could be reduced to:
+
+define i32 @mul(i32 %a, i32 %b) nounwind readnone {
+entry:
+ %tmp = mul i32 %b, %a
+ ret i32 %tmp
+}
+
+//===---------------------------------------------------------------------===//
+