From a0de7b7e046ccd809e93dd4463c4a39d157f1dbe Mon Sep 17 00:00:00 2001 From: Kohei Asano Date: Mon, 20 Feb 2023 09:38:03 +0100 Subject: [PATCH] [InstSimplify] Fold LoadInst for uniform constant global variables Fold LoadInst for uniformly initialized constants, even if there are non-constant GEP indices. Goal proof: https://alive2.llvm.org/ce/z/oZtVby Motivated by https://github.com/rust-lang/rust/issues/107208 Differential Revision: https://reviews.llvm.org/D144184 --- llvm/lib/Analysis/InstructionSimplify.cpp | 6 ++++++ llvm/test/Transforms/InstSimplify/load.ll | 9 ++------- 2 files changed, 8 insertions(+), 7 deletions(-) diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp index 38dc5fb3ee0e..9f294dfb4f20 100644 --- a/llvm/lib/Analysis/InstructionSimplify.cpp +++ b/llvm/lib/Analysis/InstructionSimplify.cpp @@ -6586,6 +6586,12 @@ static Value *simplifyLoadInst(LoadInst *LI, Value *PtrOp, if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer()) return nullptr; + // If GlobalVariable's initializer is uniform, then return the constant + // regardless of its offset. + if (Constant *C = + ConstantFoldLoadFromUniformValue(GV->getInitializer(), LI->getType())) + return C; + // Try to convert operand into a constant by stripping offsets while looking // through invariant.group intrinsics. APInt Offset(Q.DL.getIndexTypeSizeInBits(PtrOp->getType()), 0); diff --git a/llvm/test/Transforms/InstSimplify/load.ll b/llvm/test/Transforms/InstSimplify/load.ll index 40ce6f7d4dfc..21a6452960ad 100644 --- a/llvm/test/Transforms/InstSimplify/load.ll +++ b/llvm/test/Transforms/InstSimplify/load.ll @@ -48,9 +48,7 @@ define <3 x float> @load_vec3() { define i32 @load_gep_const_zero_array(i64 %idx) { ; CHECK-LABEL: @load_gep_const_zero_array( -; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds [4 x i32], ptr @constzeroarray, i64 0, i64 [[IDX:%.*]] -; CHECK-NEXT: [[LOAD:%.*]] = load i32, ptr [[GEP]], align 4 -; CHECK-NEXT: ret i32 [[LOAD]] +; CHECK-NEXT: ret i32 0 ; %gep = getelementptr inbounds [4 x i32], ptr @constzeroarray, i64 0, i64 %idx %load = load i32, ptr %gep @@ -59,10 +57,7 @@ define i32 @load_gep_const_zero_array(i64 %idx) { define i8 @load_i8_multi_gep_const_zero_array(i64 %idx1, i64 %idx2) { ; CHECK-LABEL: @load_i8_multi_gep_const_zero_array( -; CHECK-NEXT: [[GEP1:%.*]] = getelementptr inbounds i8, ptr @constzeroarray, i64 [[IDX1:%.*]] -; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr [[GEP1]], i64 [[IDX2:%.*]] -; CHECK-NEXT: [[LOAD:%.*]] = load i8, ptr [[GEP]], align 1 -; CHECK-NEXT: ret i8 [[LOAD]] +; CHECK-NEXT: ret i8 0 ; %gep1 = getelementptr inbounds i8, ptr @constzeroarray, i64 %idx1 %gep = getelementptr inbounds i8, ptr %gep1, i64 %idx2