[llvm] 1b78ff6 - [InstCombine] Simplify the pointer operand of store if writing to null is UB (#127979)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Feb 20 07:53:49 PST 2025
Author: Yingwei Zheng
Date: 2025-02-20T23:53:45+08:00
New Revision: 1b78ff6972789d189fe0b403b403626328bf6a65
URL: https://github.com/llvm/llvm-project/commit/1b78ff6972789d189fe0b403b403626328bf6a65
DIFF: https://github.com/llvm/llvm-project/commit/1b78ff6972789d189fe0b403b403626328bf6a65.diff
LOG: [InstCombine] Simplify the pointer operand of store if writing to null is UB (#127979)
Proof: https://alive2.llvm.org/ce/z/mzVj-u
I will add some follow-up patches to avoid duplicate code, support more
memory instructions, and bypass gep instructions.
Added:
llvm/test/Transforms/PhaseOrdering/load-store-sameval.ll
Modified:
llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
llvm/test/Transforms/InstCombine/store.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 4b42e86e25161..d5534c15cca76 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1437,6 +1437,20 @@ Instruction *InstCombinerImpl::visitStoreInst(StoreInst &SI) {
if (isa<UndefValue>(Val))
return eraseInstFromFunction(SI);
+ // TODO: Add a helper to simplify the pointer operand for all memory
+ // instructions.
+ // store val, (select (cond, null, P)) -> store val, P
+ // store val, (select (cond, P, null)) -> store val, P
+ if (!NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace())) {
+ if (SelectInst *Sel = dyn_cast<SelectInst>(Ptr)) {
+ if (isa<ConstantPointerNull>(Sel->getOperand(1)))
+ return replaceOperand(SI, 1, Sel->getOperand(2));
+
+ if (isa<ConstantPointerNull>(Sel->getOperand(2)))
+ return replaceOperand(SI, 1, Sel->getOperand(1));
+ }
+ }
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/store.ll b/llvm/test/Transforms/InstCombine/store.ll
index 673395464c85a..0a2b0a5ee7987 100644
--- a/llvm/test/Transforms/InstCombine/store.ll
+++ b/llvm/test/Transforms/InstCombine/store.ll
@@ -345,6 +345,48 @@ define void @store_to_readonly_noalias(ptr readonly noalias %0) {
ret void
}
+define void @store_select_with_null(i1 %cond, ptr %p) {
+; CHECK-LABEL: @store_select_with_null(
+; CHECK-NEXT: store i32 0, ptr [[SEL:%.*]], align 4
+; CHECK-NEXT: ret void
+;
+ %sel = select i1 %cond, ptr %p, ptr null
+ store i32 0, ptr %sel, align 4
+ ret void
+}
+
+define void @store_select_with_null_commuted(i1 %cond, ptr %p) {
+; CHECK-LABEL: @store_select_with_null_commuted(
+; CHECK-NEXT: store i32 0, ptr [[SEL:%.*]], align 4
+; CHECK-NEXT: ret void
+;
+ %sel = select i1 %cond, ptr null, ptr %p
+ store i32 0, ptr %sel, align 4
+ ret void
+}
+
+define void @store_select_with_null_null_is_valid(i1 %cond, ptr %p) null_pointer_is_valid {
+; CHECK-LABEL: @store_select_with_null_null_is_valid(
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr null
+; CHECK-NEXT: store i32 0, ptr [[SEL]], align 4
+; CHECK-NEXT: ret void
+;
+ %sel = select i1 %cond, ptr %p, ptr null
+ store i32 0, ptr %sel, align 4
+ ret void
+}
+
+define void @store_select_with_unknown(i1 %cond, ptr %p, ptr %p2) {
+; CHECK-LABEL: @store_select_with_unknown(
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr [[P2:%.*]]
+; CHECK-NEXT: store i32 0, ptr [[SEL]], align 4
+; CHECK-NEXT: ret void
+;
+ %sel = select i1 %cond, ptr %p, ptr %p2
+ store i32 0, ptr %sel, align 4
+ ret void
+}
+
!0 = !{!4, !4, i64 0}
!1 = !{!"omnipotent char", !2}
!2 = !{!"Simple C/C++ TBAA"}
diff --git a/llvm/test/Transforms/PhaseOrdering/load-store-sameval.ll b/llvm/test/Transforms/PhaseOrdering/load-store-sameval.ll
new file mode 100644
index 0000000000000..d8ef0723cf09e
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/load-store-sameval.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes='instcombine,early-cse<memssa>' -S %s | FileCheck %s
+
+; FIXME: We can remove the store instruction in the exit block
+define i32 @load_store_sameval(ptr %p, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: define i32 @load_store_sameval(
+; CHECK-SAME: ptr [[P:%.*]], i1 [[COND1:%.*]], i1 [[COND2:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[COND1]], ptr null, ptr [[P]]
+; CHECK-NEXT: [[PRE:%.*]] = load i32, ptr [[SPEC_SELECT]], align 4
+; CHECK-NEXT: br label %[[BLOCK:.*]]
+; CHECK: [[BLOCK]]:
+; CHECK-NEXT: br label %[[BLOCK2:.*]]
+; CHECK: [[BLOCK2]]:
+; CHECK-NEXT: br i1 [[COND2]], label %[[BLOCK3:.*]], label %[[EXIT:.*]]
+; CHECK: [[BLOCK3]]:
+; CHECK-NEXT: [[LOAD:%.*]] = load double, ptr [[SPEC_SELECT]], align 8
+; CHECK-NEXT: [[CMP:%.*]] = fcmp une double [[LOAD]], 0.000000e+00
+; CHECK-NEXT: br i1 [[CMP]], label %[[BLOCK]], label %[[BLOCK2]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: store i32 [[PRE]], ptr [[P]], align 4
+; CHECK-NEXT: ret i32 0
+;
+entry:
+ %spec.select = select i1 %cond1, ptr null, ptr %p
+ %pre = load i32, ptr %spec.select, align 4
+ br label %block
+
+block:
+ br label %block2
+
+block2:
+ br i1 %cond2, label %block3, label %exit
+
+block3:
+ %load = load double, ptr %spec.select, align 8
+ %cmp = fcmp une double %load, 0.000000e+00
+ br i1 %cmp, label %block, label %block2
+
+exit:
+ store i32 %pre, ptr %spec.select, align 4
+ ret i32 0
+}
+
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