[PATCH] D124241: [Local] Consider atomic loads from constant global as dead

[Nikita Popov via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGaae5f8115a7c: [Local] Consider atomic loads from constant global as dead (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124241/new/

https://reviews.llvm.org/D124241

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/CodeGen/PowerPC/atomics-constant.ll
  llvm/test/Transforms/InstCombine/atomic.ll


Index: llvm/test/Transforms/InstCombine/atomic.ll
===================================================================
--- llvm/test/Transforms/InstCombine/atomic.ll
+++ llvm/test/Transforms/InstCombine/atomic.ll
@@ -426,7 +426,6 @@
 
 define i32 @atomic_load_from_constant_global() {
 ; CHECK-LABEL: @atomic_load_from_constant_global(
-; CHECK-NEXT:    [[V:%.*]] = load atomic i32, i32* @c seq_cst, align 4
 ; CHECK-NEXT:    ret i32 42
 ;
   %v = load atomic i32, i32* @c seq_cst, align 4
@@ -435,7 +434,6 @@
 
 define i8 @atomic_load_from_constant_global_bitcast() {
 ; CHECK-LABEL: @atomic_load_from_constant_global_bitcast(
-; CHECK-NEXT:    [[V:%.*]] = load atomic i8, i8* bitcast (i32* @c to i8*) seq_cst, align 1
 ; CHECK-NEXT:    ret i8 42
 ;
   %v = load atomic i8, i8* bitcast (i32* @c to i8*) seq_cst, align 1
Index: llvm/test/CodeGen/PowerPC/atomics-constant.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/atomics-constant.ll
+++ llvm/test/CodeGen/PowerPC/atomics-constant.ll
@@ -3,16 +3,14 @@
 
 target triple = "powerpc64le-unknown-linux-gnu"
 
- at a = dso_local constant i64 zeroinitializer
+ at a = dso_local global i64 zeroinitializer
 
 define i64 @foo() {
 ; CHECK-LABEL: foo:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    li 4, 0
 ; CHECK-NEXT:    addis 3, 2, a at toc@ha
 ; CHECK-NEXT:    ld 3, a at toc@l(3)
-; CHECK-NEXT:    cmpd 7, 4, 4
-; CHECK-NEXT:    li 3, 0
+; CHECK-NEXT:    cmpd 7, 3, 3
 ; CHECK-NEXT:    bne- 7, .+4
 ; CHECK-NEXT:    isync
 ; CHECK-NEXT:    blr
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -500,6 +500,13 @@
     if (isMathLibCallNoop(Call, TLI))
       return true;
 
+  // Non-volatile atomic loads from constants can be removed.
+  if (auto *LI = dyn_cast<LoadInst>(I))
+    if (auto *GV = dyn_cast<GlobalVariable>(
+            LI->getPointerOperand()->stripPointerCasts()))
+      if (!LI->isVolatile() && GV->isConstant())
+        return true;
+
   return false;
 }
 


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