[llvm] c6ff3c9 - [InstSimplify] Constant fold icmp of gep

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-03-04T23:16:52+01:00
New Revision: c6ff3c9bad88d2cd027a8d0149baf1b541b84653

URL: https://github.com/llvm/llvm-project/commit/c6ff3c9bad88d2cd027a8d0149baf1b541b84653
DIFF: https://github.com/llvm/llvm-project/commit/c6ff3c9bad88d2cd027a8d0149baf1b541b84653.diff

LOG: [InstSimplify] Constant fold icmp of gep

InstSimplify can fold icmps of gep where the base pointers are the
same and the offsets are constant. It does so by constructing a
constant expression icmp and assumes that it gets folded -- but
this doesn't actually happen, because GEP expressions can usually
only be folded by the target-dependent constant folding layer.
As such, we need to explicitly invoke it here.

Differential Revision: https://reviews.llvm.org/D75407

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/compare.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index ac79031d7632..45fd6238dc86 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3481,7 +3481,8 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
         SmallVector<Value *, 4> IndicesRHS(GRHS->idx_begin(), GRHS->idx_end());
         Constant *NewRHS = ConstantExpr::getGetElementPtr(
             GLHS->getSourceElementType(), Null, IndicesRHS);
-        return ConstantExpr::getICmp(Pred, NewLHS, NewRHS);
+        Constant *NewICmp = ConstantExpr::getICmp(Pred, NewLHS, NewRHS);
+        return ConstantFoldConstant(NewICmp, Q.DL);
       }
     }
   }

diff  --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
index c4e791fc6695..3dfdaf2ecf2f 100644
--- a/llvm/test/Transforms/InstSimplify/compare.ll
+++ b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -301,7 +301,7 @@ define i1 @gep17() {
 
 define i1 @gep_same_base_constant_indices(i8* %a) {
 ; CHECK-LABEL: @gep_same_base_constant_indices(
-; CHECK-NEXT:    ret i1 icmp slt (i8* getelementptr (i8, i8* null, i64 1), i8* getelementptr (i8, i8* null, i64 10))
+; CHECK-NEXT:    ret i1 true
 ;
   %arrayidx1 = getelementptr inbounds i8, i8* %a, i64 1
   %arrayidx2 = getelementptr inbounds i8, i8* %a, i64 10