[PATCH] D72060: [InstCombine] Preseve inbounds when merging with zero-index GEP (PR44423)

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: lebedev.ri, spatel, RKSimon.
Herald added subscribers: llvm-commits, arphaman, hiraditya.
Herald added a project: LLVM.

This addresses https://bugs.llvm.org/show_bug.cgi?id=44423. If one of the GEPs is inbounds and the other is zero-index, we can also preserve inbounds.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72060

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/getelementptr.ll


Index: llvm/test/Transforms/InstCombine/getelementptr.ll
===================================================================
--- llvm/test/Transforms/InstCombine/getelementptr.ll
+++ llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -1171,7 +1171,7 @@
 
 define i32* @test_bitcast_nzgep([1 x i32]* %base, i64 %idx) {
 ; CHECK-LABEL: @test_bitcast_nzgep(
-; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]
 ; CHECK-NEXT:    ret i32* [[PTR]]
 ;
   %base2 = bitcast [1 x i32]* %base to i32*
@@ -1181,7 +1181,7 @@
 
 define i32* @test_zgep_nzgep([1 x i32]* %base, i64 %idx) {
 ; CHECK-LABEL: @test_zgep_nzgep(
-; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 0, i64 [[IDX:%.*]]
 ; CHECK-NEXT:    ret i32* [[PTR]]
 ;
   %base2 = getelementptr [1 x i32], [1 x i32]* %base, i64 0, i64 0
@@ -1191,7 +1191,7 @@
 
 define i32* @test_nzgep_zgep([1 x i32]* %base, i64 %idx) {
 ; CHECK-LABEL: @test_nzgep_zgep(
-; CHECK-NEXT:    [[PTR:%.*]] = getelementptr [1 x i32], [1 x i32]* [[BASE:%.*]], i64 [[IDX:%.*]], i64 0
+; CHECK-NEXT:    [[PTR:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[BASE:%.*]], i64 [[IDX:%.*]], i64 0
 ; CHECK-NEXT:    ret i32* [[PTR]]
 ;
   %base2 = getelementptr inbounds [1 x i32], [1 x i32]* %base, i64 %idx
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1649,6 +1649,15 @@
   return CastInst::Create(CastOpc, NarrowBO, BO.getType());
 }
 
+bool isMergedGEPInBounds(GEPOperator &GEP1, GEPOperator &GEP2) {
+  // At least one GEP must be inbounds.
+  if (!GEP1.isInBounds() && !GEP2.isInBounds())
+    return false;
+
+  return (GEP1.isInBounds() || GEP1.hasAllZeroIndices()) &&
+         (GEP2.isInBounds() || GEP2.hasAllZeroIndices());
+}
+
 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
   Type *GEPType = GEP.getType();
@@ -1922,7 +1931,7 @@
 
       // Update the GEP in place if possible.
       if (Src->getNumOperands() == 2) {
-        GEP.setIsInBounds(GEP.isInBounds() && Src->isInBounds());
+        GEP.setIsInBounds(isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP)));
         GEP.setOperand(0, Src->getOperand(0));
         GEP.setOperand(1, Sum);
         return &GEP;
@@ -1939,7 +1948,7 @@
     }
 
     if (!Indices.empty())
-      return GEP.isInBounds() && Src->isInBounds()
+      return isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP))
                  ? GetElementPtrInst::CreateInBounds(
                        Src->getSourceElementType(), Src->getOperand(0), Indices,
                        GEP.getName())


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D72060.235795.patch
Type: text/x-patch
Size: 3082 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200101/325b518d/attachment.bin>