[PATCH] D144184: [InstSimplify] fold LoadInst for uniformaly initialized constant global variables

[Kohei Asano via Phabricator via llvm-commits]

khei4 updated this revision to Diff 498708.
khei4 added a comment.

I noticed mistakenly reverted the review fix. Rebase.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144184/new/

https://reviews.llvm.org/D144184

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/load.ll


Index: llvm/test/Transforms/InstSimplify/load.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/load.ll
+++ llvm/test/Transforms/InstSimplify/load.ll
@@ -4,6 +4,12 @@
 @zeroinit = constant {} zeroinitializer
 @poison = constant {} poison
 
+
+ at constzeroarray = internal constant [4 x i32] zeroinitializer
+
+ at constarray = internal constant [4 x i32] [i32 1, i32 1, i32 1, i32 1]
+ at constarrayi8 = internal constant [2 x i8] [i8 1, i8 1]
+
 define i32 @crash_on_zeroinit() {
 ; CHECK-LABEL: @crash_on_zeroinit(
 ; CHECK-NEXT:    ret i32 poison
@@ -40,3 +46,46 @@
   %1 = load <3 x float>, ptr getelementptr inbounds (<3 x float>, ptr @constvec, i64 1)
   ret <3 x float> %1
 }
+
+define i32 @load_gep_const_zero_array(i64 %idx) {
+; CHECK-LABEL: @load_gep_const_zero_array(
+; CHECK-NEXT:    ret i32 0
+;
+  %gep = getelementptr inbounds [4 x i32], ptr @constzeroarray, i64 0, i64 %idx
+  %load = load i32, ptr %gep
+  ret i32 %load
+}
+
+define i8 @load_i8_multi_gep_const_zero_array(i64 %idx1, i64 %idx2) {
+; CHECK-LABEL: @load_i8_multi_gep_const_zero_array(
+; CHECK-NEXT:    ret i8 0
+;
+  %gep1 = getelementptr inbounds i8, ptr @constzeroarray, i64 %idx1
+  %gep = getelementptr inbounds i8, ptr %gep1, i64 %idx2
+  %load = load i8, ptr %gep
+  ret i8 %load
+}
+
+define i32 @load_gep_const_array(i64 %idx) {
+; CHECK-LABEL: @load_gep_const_array(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds [4 x i32], ptr @constarray, i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[GEP]], align 4
+; CHECK-NEXT:    ret i32 [[LOAD]]
+;
+  %gep = getelementptr inbounds [4 x i32], ptr @constarray, i64 0, i64 %idx
+  %load = load i32, ptr %gep
+  ret i32 %load
+}
+
+define i8 @load_i8_multi_gep_const_array(i64 %idx1, i64 %idx2) {
+; CHECK-LABEL: @load_i8_multi_gep_const_array(
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr inbounds i8, ptr @constarrayi8, 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]]
+;
+  %gep1 = getelementptr inbounds i8, ptr @constarrayi8, i64 %idx1
+  %gep = getelementptr inbounds i8, ptr %gep1, i64 %idx2
+  %load = load i8, ptr %gep
+  ret i8 %load
+}
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -6586,6 +6586,12 @@
   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);


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