[llvm] 289542b - [InstCombine] Fold icmp eq of non-inbounds geps

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-03-21T10:51:37+01:00
New Revision: 289542b1e72dc4fe17093952dfb1b04cce259183

URL: https://github.com/llvm/llvm-project/commit/289542b1e72dc4fe17093952dfb1b04cce259183
DIFF: https://github.com/llvm/llvm-project/commit/289542b1e72dc4fe17093952dfb1b04cce259183.diff

LOG: [InstCombine] Fold icmp eq of non-inbounds geps

We can fold equality comparisons of non-inbounds geps to offset
comparison (https://alive2.llvm.org/ce/z/x2Zp8b). The inbounds
requirement is only necessary for relational comparisons.

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index b9473634e6dc..421b1824b965 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -884,7 +884,8 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
 
     // Only lower this if the icmp is the only user of the GEP or if we expect
     // the result to fold to a constant!
-    if (GEPsInBounds && (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
+    if ((GEPsInBounds || CmpInst::isEquality(Cond)) &&
+        (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
         (isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
       // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)  --->  (OFFSET1 cmp OFFSET2)
       Value *L = EmitGEPOffset(GEPLHS);

diff  --git a/llvm/test/Transforms/InstCombine/icmp-gep.ll b/llvm/test/Transforms/InstCombine/icmp-gep.ll
index 5fef7ac43536..5cc6d9f80bac 100644
--- a/llvm/test/Transforms/InstCombine/icmp-gep.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-gep.ll
@@ -299,9 +299,8 @@ define i1 @test_gep_ult_no_inbounds(ptr %foo, i64 %i, i64 %j) {
 
 define i1 @test_gep_eq_no_inbounds(ptr %foo, i64 %i, i64 %j) {
 ; CHECK-LABEL: @test_gep_eq_no_inbounds(
-; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr i32, ptr [[FOO:%.*]], i64 [[I:%.*]]
-; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i8, ptr [[FOO]], i64 [[J:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[GEP1]], [[GEP2]]
+; CHECK-NEXT:    [[GEP1_IDX:%.*]] = shl i64 [[I:%.*]], 2
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[GEP1_IDX]], [[J:%.*]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %gep1 = getelementptr i32, ptr %foo, i64 %i