[llvm] r259375 - [InstCombine] Don't transform (X+INT_MAX)>=(Y+INT_MAX) -> (X<=Y)

[David Majnemer via llvm-commits]

Author: majnemer
Date: Mon Feb  1 11:37:56 2016
New Revision: 259375

URL: http://llvm.org/viewvc/llvm-project?rev=259375&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=259375&r1=259374&r2=259375&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Mon Feb  1 11:37:56 2016
@@ -3877,7 +3877,7 @@ Instruction *InstCombiner::visitICmpInst
                                 BO1->getOperand(0));
           }
 
-          if (CI->isMaxValue(true)) {
+          if (BO0->getOpcode() == Instruction::Xor && CI->isMaxValue(true)) {
             ICmpInst::Predicate Pred = I.isSigned()
                                            ? I.getUnsignedPredicate()
                                            : I.getSignedPredicate();

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=259375&r1=259374&r2=259375&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Mon Feb  1 11:37:56 2016
@@ -1672,3 +1672,15 @@ define i1 @cmp_slt_rhs_inc(float %x, i32
   %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
+}