CMOV_GR8 clobbers EFLAGS when its expansion involves an xor to set

a register to 0. This fixes PR4814.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80445 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index e76031039529f77f722d099f8849111fda6d0f8d..056335f167e9612f6575766b599644f25356d73c 100644 (file)
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -1038,8 +1038,10 @@ let Uses = [EFLAGS] in {
 // X86 doesn't have 8-bit conditional moves. Use a customDAGSchedInserter to
 // emit control flow. An alternative to this is to mark i8 SELECT as Promote,
 // however that requires promoting the operands, and can induce additional
-// i8 register pressure.
-let usesCustomDAGSchedInserter = 1, isTwoAddress = 0 in
+// i8 register pressure. Note that CMOV_GR8 is conservatively considered to
+// clobber EFLAGS, because if one of the operands is zero, the expansion
+// could involve an xor.
+let usesCustomDAGSchedInserter = 1, isTwoAddress = 0, Defs = [EFLAGS] in
 def CMOV_GR8 : I<0, Pseudo,
                  (outs GR8:$dst), (ins GR8:$src1, GR8:$src2, i8imm:$cond),
                  "#CMOV_GR8 PSEUDO!",

diff --git a/test/CodeGen/X86/cmov-i8-eflags.ll b/test/CodeGen/X86/cmov-i8-eflags.ll
new file mode 100644 (file)
index 0000000..e81ce58
--- /dev/null
+++ b/test/CodeGen/X86/cmov-i8-eflags.ll
@@ -0,0 +1,55 @@
+; RUN: llvm-as < %s | llc -march=x86-64 | %prcontext {setne    %al} 1 | grep test | count 2
+; PR4814
+
+; CodeGen shouldn't try to do a setne after an expanded 8-bit conditional
+; move without recomputing EFLAGS, because the expansion of the conditional
+; move with control flow may clobber EFLAGS (e.g., with xor, to set the
+; register to zero).
+
+; The prcontext usage above is a little awkward; the important part is that
+; there's a test before the setne.
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+
+@g_3 = external global i8                         ; <i8*> [#uses=1]
+@g_96 = external global i8                        ; <i8*> [#uses=2]
+@g_100 = external global i8                       ; <i8*> [#uses=2]
+@_2E_str = external constant [15 x i8], align 1   ; <[15 x i8]*> [#uses=1]
+
+define i32 @main() nounwind {
+entry:
+  %0 = load i8* @g_3, align 1                     ; <i8> [#uses=2]
+  %1 = sext i8 %0 to i32                          ; <i32> [#uses=1]
+  %.lobit.i = lshr i8 %0, 7                       ; <i8> [#uses=1]
+  %tmp.i = zext i8 %.lobit.i to i32               ; <i32> [#uses=1]
+  %tmp.not.i = xor i32 %tmp.i, 1                  ; <i32> [#uses=1]
+  %iftmp.17.0.i.i = ashr i32 %1, %tmp.not.i       ; <i32> [#uses=1]
+  %retval56.i.i = trunc i32 %iftmp.17.0.i.i to i8 ; <i8> [#uses=1]
+  %2 = icmp eq i8 %retval56.i.i, 0                ; <i1> [#uses=2]
+  %g_96.promoted.i = load i8* @g_96               ; <i8> [#uses=3]
+  %3 = icmp eq i8 %g_96.promoted.i, 0             ; <i1> [#uses=2]
+  br i1 %3, label %func_4.exit.i, label %bb.i.i.i
+
+bb.i.i.i:                                         ; preds = %entry
+  %4 = volatile load i8* @g_100, align 1          ; <i8> [#uses=0]
+  br label %func_4.exit.i
+
+func_4.exit.i:                                    ; preds = %bb.i.i.i, %entry
+  %.not.i = xor i1 %2, true                       ; <i1> [#uses=1]
+  %brmerge.i = or i1 %3, %.not.i                  ; <i1> [#uses=1]
+  %.mux.i = select i1 %2, i8 %g_96.promoted.i, i8 0 ; <i8> [#uses=1]
+  br i1 %brmerge.i, label %func_1.exit, label %bb.i.i
+
+bb.i.i:                                           ; preds = %func_4.exit.i
+  %5 = volatile load i8* @g_100, align 1          ; <i8> [#uses=0]
+  br label %func_1.exit
+
+func_1.exit:                                      ; preds = %bb.i.i, %func_4.exit.i
+  %g_96.tmp.0.i = phi i8 [ %g_96.promoted.i, %bb.i.i ], [ %.mux.i, %func_4.exit.i ] ; <i8> [#uses=2]
+  store i8 %g_96.tmp.0.i, i8* @g_96
+  %6 = zext i8 %g_96.tmp.0.i to i32               ; <i32> [#uses=1]
+  %7 = tail call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([15 x i8]* @_2E_str, i64 0, i64 0), i32 %6) nounwind ; <i32> [#uses=0]
+  ret i32 0
+}
+
+declare i32 @printf(i8* nocapture, ...) nounwind