[InstCombine] Don't transform (X+INT_MAX)>=(Y+INT_MAX) -> (X<=Y)

This miscompile came about because we tried to use a transform which was
only appropriate for xor operators when addition was present.

This fixes PR26407.

llvm-svn: 259375

2 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index f322e4ed7aa..051fd1084f7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3877,7 +3877,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
                                 BO1->getOperand(0));
           }
 
-          if (CI->isMaxValue(true)) {
+          if (BO0->getOpcode() == Instruction::Xor && CI->isMaxValue(true)) {
             ICmpInst::Predicate Pred = I.isSigned()
                                            ? I.getUnsignedPredicate()
                                            : I.getSignedPredicate();
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 7d6ec96b532..1e64cd7f582 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -1672,3 +1672,15 @@ define i1 @cmp_slt_rhs_inc(float %x, i32 %i) {
   %cmp = icmp slt i32 %conv, %inc
   ret i1 %cmp
 }
+
+; CHECK-LABEL: @PR26407
+; CHECK-NEXT: %[[addx:.*]] = add i32 %x, 2147483647
+; CHECK-NEXT: %[[addy:.*]] = add i32 %y, 2147483647
+; CHECK-NEXT: %[[cmp:.*]] = icmp uge i32 %[[addx]], %[[addy]]
+; CHECK-NEXT: ret i1 %[[cmp]]
+define i1 @PR26407(i32 %x, i32 %y) {
+  %addx = add i32 %x, 2147483647
+  %addy = add i32 %y, 2147483647
+  %cmp = icmp uge i32 %addx, %addy
+  ret i1 %cmp
+}