[llvm] 95fedfa - [InstCombine] Handle non-canonical GEP index in indexed compare fold (PR55228)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-05-02T17:56:01+02:00
New Revision: 95fedfab6cfb82a2fe1010d266b1269425f5eb46

URL: https://github.com/llvm/llvm-project/commit/95fedfab6cfb82a2fe1010d266b1269425f5eb46
DIFF: https://github.com/llvm/llvm-project/commit/95fedfab6cfb82a2fe1010d266b1269425f5eb46.diff

LOG: [InstCombine] Handle non-canonical GEP index in indexed compare fold (PR55228)

Normally the index type will already be canonicalized here, but
this is not guaranteed depending on visitation order. The code
was already accounting for a potentially needed sext, but a trunc
may also be needed.

Add a ConstantExpr::getSExtOrTrunc() helper method to make this
simpler. This matches the corresponding IRBuilder method in behavior.

Fixes https://github.com/llvm/llvm-project/issues/55228.

Added: 
    llvm/test/Transforms/InstCombine/pr55228.ll

Modified: 
    llvm/include/llvm/IR/Constants.h
    llvm/lib/IR/Constants.cpp
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/IR/Constants.h b/llvm/include/llvm/IR/Constants.h
index fb884912b318b..6c655407cb5e0 100644
--- a/llvm/include/llvm/IR/Constants.h
+++ b/llvm/include/llvm/IR/Constants.h
@@ -1160,6 +1160,11 @@ class ConstantExpr : public Constant {
                     Type *Ty     ///< The type to trunc or bitcast C to
   );
 
+  /// Create either an sext, trunc or nothing, depending on whether Ty is
+  /// wider, narrower or the same as C->getType(). This only works with
+  /// integer or vector of integer types.
+  static Constant *getSExtOrTrunc(Constant *C, Type *Ty);
+
   /// Create a BitCast, AddrSpaceCast, or a PtrToInt cast constant
   /// expression.
   static Constant *

diff  --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 5dcf1bab1dbb5..c182513fc1d14 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -2068,6 +2068,17 @@ Constant *ConstantExpr::getTruncOrBitCast(Constant *C, Type *Ty) {
   return getTrunc(C, Ty);
 }
 
+Constant *ConstantExpr::getSExtOrTrunc(Constant *C, Type *Ty) {
+  assert(C->getType()->isIntOrIntVectorTy() && Ty->isIntOrIntVectorTy() &&
+         "Can only sign extend/truncate integers!");
+  Type *CTy = C->getType();
+  if (CTy->getScalarSizeInBits() < Ty->getScalarSizeInBits())
+    return getSExt(C, Ty);
+  if (CTy->getScalarSizeInBits() > Ty->getScalarSizeInBits())
+    return getTrunc(C, Ty);
+  return C;
+}
+
 Constant *ConstantExpr::getPointerCast(Constant *S, Type *Ty) {
   assert(S->getType()->isPtrOrPtrVectorTy() && "Invalid cast");
   assert((Ty->isIntOrIntVectorTy() || Ty->isPtrOrPtrVectorTy()) &&

diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 4a62afce19be9..39a32e526d714 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -759,7 +759,7 @@ getAsConstantIndexedAddress(Type *ElemTy, Value *V, const DataLayout &DL) {
         V = GEP->getOperand(0);
         Constant *GEPIndex = static_cast<Constant *>(GEP->getOperand(1));
         Index = ConstantExpr::getAdd(
-            Index, ConstantExpr::getSExtOrBitCast(GEPIndex, IndexType));
+            Index, ConstantExpr::getSExtOrTrunc(GEPIndex, IndexType));
         continue;
       }
       break;

diff  --git a/llvm/test/Transforms/InstCombine/pr55228.ll b/llvm/test/Transforms/InstCombine/pr55228.ll
new file mode 100644
index 0000000000000..5ef9f00035da2
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr55228.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+target datalayout = "p:8:8"
+
+ at g = external global i8
+ at c = constant ptr getelementptr inbounds (i8, ptr @g, i64 1)
+
+define i1 @test(ptr %p) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq ptr [[P:%.*]], getelementptr inbounds (i8, ptr @g, i8 1)
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %alloca = alloca ptr
+  call void @llvm.memcpy.p0.p0.i32(ptr %alloca, ptr @c, i32 0, i1 false)
+  %load = load ptr, ptr %alloca
+  %cmp = icmp eq ptr %p, %load
+  ret i1 %cmp
+}
+
+declare void @llvm.memcpy.p0.p0.i32(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i32, i1 immarg)