[PATCH] D130277: [ConstantFold] Fold non-zero index GEP_GV vs GV comparison

[luxufan via Phabricator via llvm-commits]

StephenFan created this revision.
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When comparing non-zero index GEP_GV and GV, if GEP's offset less than
the size of GEP's GV and is non-negative, we can try to fold this comparison.

Fixes https://github.com/llvm/llvm-project/issues/48778


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D130277

Files:
  llvm/lib/IR/ConstantFold.cpp
  llvm/test/Other/constant-fold-gep.ll
  llvm/test/Transforms/InstCombine/hoist-xor-by-constant-from-xor-by-value.ll


Index: llvm/test/Transforms/InstCombine/hoist-xor-by-constant-from-xor-by-value.ll
===================================================================
--- llvm/test/Transforms/InstCombine/hoist-xor-by-constant-from-xor-by-value.ll
+++ llvm/test/Transforms/InstCombine/hoist-xor-by-constant-from-xor-by-value.ll
@@ -96,7 +96,7 @@
 ; CHECK-LABEL: @constantexpr2(
 ; CHECK-NEXT:    [[I2:%.*]] = load i16*, i16** @global_constant5, align 1
 ; CHECK-NEXT:    [[I3:%.*]] = load i16, i16* [[I2]], align 1
-; CHECK-NEXT:    [[I5:%.*]] = xor i16 [[I3]], xor (i16 zext (i1 icmp ne (i64* getelementptr inbounds ([6 x [1 x i64]], [6 x [1 x i64]]* @global_constant3, i64 0, i64 5, i64 0), i64* @global_constant4) to i16), i16 -1)
+; CHECK-NEXT:    [[I5:%.*]] = xor i16 [[I3]], -2
 ; CHECK-NEXT:    ret i16 [[I5]]
 ;
   %i0 = icmp ne i64* getelementptr inbounds ([6 x [1 x i64]], [6 x [1 x i64]]* @global_constant3, i16 0, i16 5, i16 0), @global_constant4
Index: llvm/test/Other/constant-fold-gep.ll
===================================================================
--- llvm/test/Other/constant-fold-gep.ll
+++ llvm/test/Other/constant-fold-gep.ll
@@ -470,6 +470,7 @@
 @gv1 = internal global i32 1
 @gv2 = internal global [1 x i32] [ i32 2 ]
 @gv3 = internal global [1 x i32] [ i32 2 ]
+ at gv4 = internal global [2 x i32] [ i32 2, i32 2 ]
 
 ; Handled by TI-independent constant folder
 define i1 @gv_gep_vs_gv() {
@@ -478,6 +479,12 @@
 ; PLAIN: gv_gep_vs_gv
 ; PLAIN: ret i1 false
 
+define i1 @gv_gep_vs_gv_non_zero() {
+  ret i1 icmp eq (i32* getelementptr inbounds ([2 x i32], [2 x i32]* @gv4, i32 0, i32 1), i32* @gv1)
+}
+; PLAIN: gv_gep_vs_gv_non_zero
+; PLAIN: ret i1 false
+
 define i1 @gv_gep_vs_gv_gep() {
   ret i1 icmp eq (i32* getelementptr inbounds ([1 x i32], [1 x i32]* @gv2, i32 0, i32 0), i32* getelementptr inbounds ([1 x i32], [1 x i32]* @gv3, i32 0, i32 0))
 }
Index: llvm/lib/IR/ConstantFold.cpp
===================================================================
--- llvm/lib/IR/ConstantFold.cpp
+++ llvm/lib/IR/ConstantFold.cpp
@@ -1551,6 +1551,16 @@
           if (GV != GV2) {
             if (CE1GEP->hasAllZeroIndices())
               return areGlobalsPotentiallyEqual(GV, GV2);
+
+            const DataLayout &DL = GV->getParent()->getDataLayout();
+            TypeSize ValueSize =
+                GV->getParent()->getDataLayout().getTypeAllocSize(
+                    GV->getValueType());
+            APInt Offset(DL.getIndexTypeSizeInBits(CE1GEP->getType()), 0);
+            if (CE1GEP->accumulateConstantOffset(DL, Offset) &&
+                Offset.isNonNegative() && Offset.ult(ValueSize))
+              return areGlobalsPotentiallyEqual(GV, GV2);
+
             return ICmpInst::BAD_ICMP_PREDICATE;
           }
         }


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