[PATCH] D32970: [InstCombine] restrict icmp fold with 2 sdiv exact operands (PR32949)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added a subscriber: mcrosier.

This is the InstCombine counterpart to https://reviews.llvm.org/D32954. I added some comments about the code duplication in:
https://reviews.llvm.org/rL302436

Alive-based verification:
http://rise4fun.com/Alive/dPw

This is a 2nd fix for the problem reported in:
https://bugs.llvm.org/show_bug.cgi?id=32949


https://reviews.llvm.org/D32970

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/icmp.ll


Index: test/Transforms/InstCombine/icmp.ll
===================================================================
--- test/Transforms/InstCombine/icmp.ll
+++ test/Transforms/InstCombine/icmp.ll
@@ -695,11 +695,13 @@
   ret i1 %C
 }
 
-; FIXME: The above transform only works for equality predicates.
+; The above transform only works for equality predicates.
 
 define i1 @PR32949(i32 %X, i32 %Y, i32 %Z) {
 ; CHECK-LABEL: @PR32949(
-; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 %X, %Y
+; CHECK-NEXT:    [[A:%.*]] = sdiv exact i32 %X, %Z
+; CHECK-NEXT:    [[B:%.*]] = sdiv exact i32 %Y, %Z
+; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[A]], [[B]]
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %A = sdiv exact i32 %X, %Z
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3068,16 +3068,23 @@
         }
       }
       break;
+
     case Instruction::UDiv:
     case Instruction::LShr:
-      if (I.isSigned())
+      if (I.isSigned() || !BO0->isExact() || !BO1->isExact())
         break;
-      LLVM_FALLTHROUGH;
+      return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
+
     case Instruction::SDiv:
+      if (!I.isEquality() || !BO0->isExact() || !BO1->isExact())
+        break;
+      return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
+
     case Instruction::AShr:
       if (!BO0->isExact() || !BO1->isExact())
         break;
       return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
+
     case Instruction::Shl: {
       bool NUW = BO0->hasNoUnsignedWrap() && BO1->hasNoUnsignedWrap();
       bool NSW = BO0->hasNoSignedWrap() && BO1->hasNoSignedWrap();


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