[PATCH] D138637: [InstCombine] Combine opaque pointer single index GEP and with src GEP which has result of array type

[krishna chaitanya sankisa via Phabricator via llvm-commits]

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Removing zero indices opaque pointer gep, link <https://reviews.llvm.org/rG87a0b1bd233a3680c32a6e17acf147d0fe90c9e9>, has caused Instcombine pass to not combine few GepOfGep instructions which were previously possible for non-opaque pointers case.

Consider below IR : link <https://llvm.godbolt.org/z/ec6aTxdo5>

  @ext = external hidden global [2 x [1 x float]]
  %a = getelementptr inbounds [2 x [1 x float]], [2 x [1 x float]]* @ext, i64 0, i64 %c
  %b = getelementptr inbounds [1 x float], [1 x float]* %a, i64 0, i64 0 
  %c = getelementptr inbounds float, float* %b, i64 %in1

would be optimized to

  %c = getelementptr inbounds [2 x [1 x float]], [2 x [1 x float]]* @ext, i64 0, i64 %c, i64 %in1

This is currently not happening for opaque pointer case. link <https://llvm.godbolt.org/z/GMWbsvGoE>

This patch tries to address this issue by combining single index gep with src gep of array type.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138637

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/opaque-ptr-gep-of-gep.ll


Index: llvm/test/Transforms/InstCombine/opaque-ptr-gep-of-gep.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/opaque-ptr-gep-of-gep.ll
@@ -0,0 +1,55 @@
+; RUN: opt -S -instcombine -opaque-pointers < %s | FileCheck %s
+
+ at ext1 = external hidden global [2 x [1 x float]]
+ at ext2 = external hidden global [2 x [2 x [1 x float]]]
+
+define void @gepofgep1(i64 %in1, i64 %in2, ptr %out) {
+; CHECK-LABEL: @gepofgep1(
+; CHECK-NEXT:   [[B:%.*]] = getelementptr inbounds [2 x [1 x float]], ptr [[EXT1:@.*]], i64 0, i64 [[IN1:%.*]], i64 [[IN2:%.*]]
+; CHECK-NEXT:   store ptr [[B]], ptr [[OUT:%.*]], align 8
+; CHECK-NEXT:   ret void
+
+  %a = getelementptr inbounds [2 x [1 x float]], ptr @ext1, i64 0, i64 %in1
+  %b = getelementptr inbounds float, ptr %a, i64 %in2
+  store ptr %b, ptr %out
+  ret void
+}
+
+define void @gepofgep2(i64 %in1, i64 %in2, ptr %out) {
+; CHECK-LABEL: @gepofgep2(
+; CHECK-NEXT:   [[A:%.*]] = getelementptr inbounds [2 x [2 x [1 x float]]], ptr [[EXT2:@.*]], i64 0, i64 [[IN1:%.*]]
+; CHECK-NEXT:   [[B:%.*]] = getelementptr inbounds [1 x float], ptr [[A]], i64 0, i64 [[IN2:%.*]]
+; CHECK-NEXT:   store ptr [[B]], ptr [[OUT:%.*]], align 8
+; CHECK-NEXT:   ret void
+  %a = getelementptr inbounds [2 x [2 x [1 x float]]], ptr @ext2, i64 0, i64 %in1
+  %b = getelementptr inbounds [1 x float], ptr %a, i64 0, i64 %in2
+  store ptr %b, ptr %out
+  ret void
+}
+
+define void @gepofgep3(i64 %in1, i64 %in2, ptr %out) {
+; CHECK-LABEL: @gepofgep3(
+; CHECK-NEXT:   [[B:%.*]] = getelementptr inbounds [2 x [2 x [1 x float]]], ptr [[EXT2:@.*]], i64 [[IN1:%.*]], i64 [[IN2:%.*]]
+; CHECK-NEXT:   store ptr [[B]], ptr [[OUT:%.*]], align 8
+; CHECK-NEXT:   ret void
+  %a = getelementptr inbounds [2 x [2 x [1 x float]]], ptr @ext2, i64 %in1
+  %b = getelementptr inbounds float, ptr %a, i64 %in2
+  store ptr %b, ptr %out
+  ret void
+}
+
+define void @gepofgep4(i64 %in1, i64 %in2, ptr %out1, ptr %out2) {
+; CHECK-LABEL: @gepofgep4(
+; CHECK-NEXT:   [[B:%.*]] = getelementptr inbounds [2 x [1 x float]], ptr [[EXT1:@.*]], i64 0, i64 [[IN1:%.*]], i64 [[IN1]]
+; CHECK-NEXT:   [[C:%.*]] = getelementptr inbounds [2 x [1 x float]], ptr [[EXT1:@.*]], i64 0, i64 [[IN1]], i64 [[IN2:%.*]]
+; CHECK-NEXT:   store ptr [[B]], ptr [[OUT1:%.*]], align 8
+; CHECK-NEXT:   store ptr [[C]], ptr [[OUT2:%.*]], align 8
+; CHECK-NEXT:   ret void
+
+  %a = getelementptr inbounds [2 x [1 x float]], ptr @ext1, i64 0, i64 %in1
+  %b = getelementptr inbounds float, ptr %a, i64 %in1
+  %c = getelementptr inbounds float, ptr %a, i64 %in2
+  store ptr %b, ptr %out1
+  store ptr %c, ptr %out2
+  ret void
+}
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2109,6 +2109,24 @@
                                            GEP.getName());
   }
 
+  // Combine opaque pointer GEPs having source array type with
+  // GEP having single index.
+  if (PtrTy->isOpaquePointerTy() && Src->getResultElementType()->isArrayTy() &&
+      GEP.getNumIndices() == 1) {
+    SmallVector<Value *, 16> NewIndices;
+    NewIndices.reserve(Src->getNumIndices() + GEP.getNumIndices());
+    NewIndices.append(Src->idx_begin(), Src->idx_end());
+    NewIndices.append(GEP.idx_begin(), GEP.idx_end());
+    bool IsInBounds = isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP));
+    return IsInBounds
+               ? GetElementPtrInst::CreateInBounds(Src->getSourceElementType(),
+                                                   Src->getOperand(0),
+                                                   NewIndices, GEP.getName())
+               : GetElementPtrInst::Create(Src->getSourceElementType(),
+                                           Src->getOperand(0), NewIndices,
+                                           GEP.getName());
+  }
+
   if (Src->getResultElementType() != GEP.getSourceElementType())
     return nullptr;
 


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