Fix an overaggressive SimplifyDemandedBits optimization on urem. This

fixes the 254.gap regression on x86 and the 403.gcc regression on x86-64.

llvm-svn: 50537

2 files changed, 37 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 507e6f2a854..ce052f724e8 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1762,11 +1762,12 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask,
 
     APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0);
     APInt AllOnes = APInt::getAllOnesValue(BitWidth);
-    ComputeMaskedBits(I->getOperand(0), AllOnes,
-                      KnownZero2, KnownOne2, Depth+1);
+    if (SimplifyDemandedBits(I->getOperand(0), AllOnes,
+                             KnownZero2, KnownOne2, Depth+1))
+      return true;
+
     uint32_t Leaders = KnownZero2.countLeadingOnes();
-    APInt HighZeros = APInt::getHighBitsSet(BitWidth, Leaders);
-    if (SimplifyDemandedBits(I->getOperand(1), ~HighZeros,
+    if (SimplifyDemandedBits(I->getOperand(1), AllOnes,
                              KnownZero2, KnownOne2, Depth+1))
       return true;
 
diff --git a/llvm/test/Transforms/InstCombine/urem-simplify-bug.ll b/llvm/test/Transforms/InstCombine/urem-simplify-bug.ll
new file mode 100644
index 00000000000..15956f26b69
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/urem-simplify-bug.ll
@@ -0,0 +1,32 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {= or i32 %x, -5	}
+
+@.str = internal constant [5 x i8] c"foo\0A\00"		; <[5 x i8]*> [#uses=1]
+@.str1 = internal constant [5 x i8] c"bar\0A\00"		; <[5 x i8]*> [#uses=1]
+
+define i32 @main() nounwind  {
+entry:
+	%x = call i32 @func_11( ) nounwind 		; <i32> [#uses=1]
+	%tmp3 = or i32 %x, -5		; <i32> [#uses=1]
+	%tmp5 = urem i32 251, %tmp3		; <i32> [#uses=1]
+	%tmp6 = icmp ne i32 %tmp5, 0		; <i1> [#uses=1]
+	%tmp67 = zext i1 %tmp6 to i32		; <i32> [#uses=1]
+	%tmp9 = urem i32 %tmp67, 95		; <i32> [#uses=1]
+	%tmp10 = and i32 %tmp9, 1		; <i32> [#uses=1]
+	%tmp12 = icmp eq i32 %tmp10, 0		; <i1> [#uses=1]
+	br i1 %tmp12, label %bb14, label %bb
+
+bb:		; preds = %entry
+	br label %bb15
+
+bb14:		; preds = %entry
+	br label %bb15
+
+bb15:		; preds = %bb14, %bb
+	%iftmp.0.0 = phi i8* [ getelementptr ([5 x i8]* @.str1, i32 0, i32 0), %bb14 ], [ getelementptr ([5 x i8]* @.str, i32 0, i32 0), %bb ]		; <i8*> [#uses=1]
+	%tmp17 = call i32 (i8*, ...)* @printf( i8* %iftmp.0.0 ) nounwind 		; <i32> [#uses=0]
+	ret i32 0
+}
+
+declare i32 @func_11()
+
+declare i32 @printf(i8*, ...) nounwind