PR9346: Prevent SimplifyDemandedBits from incorrectly introducing

INT_MIN % -1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127306 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index b12d4c368740237e0647dc48848b20fd44ba5d81..6e727ce6e35c0787d64d6183f92c96bb46b1a1cc 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -684,6 +684,10 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     break;
   case Instruction::SRem:
     if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      // X % -1 demands all the bits because we don't want to introduce
+      // INT_MIN % -1 (== undef) by accident.
+      if (Rem->isAllOnesValue())
+        break;
       APInt RA = Rem->getValue().abs();
       if (RA.isPowerOf2()) {
         if (DemandedMask.ult(RA))    // srem won't affect demanded bits

diff --git a/test/Transforms/InstCombine/2011-03-08-SRemMinusOneBadOpt.ll b/test/Transforms/InstCombine/2011-03-08-SRemMinusOneBadOpt.ll
new file mode 100644 (file)
index 0000000..6a3e3e4
--- /dev/null
+++ b/test/Transforms/InstCombine/2011-03-08-SRemMinusOneBadOpt.ll
@@ -0,0 +1,12 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; PR9346
+
+define i32 @test(i64 %x) nounwind {
+; CHECK: ret i32 0
+entry:
+  %or = or i64 %x, 4294967294
+  %conv = trunc i64 %or to i32
+  %rem.i = srem i32 %conv, -1
+  ret i32 %rem.i
+}
+