[InstCombine] Increase recursion limit to 3 in simplifyNonNullOperand

[dtcxzyw]

Address review comment #128466 (comment)

Compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=72781f58efddecee19feb07fec4e6104ef4c4812&to=3853aee61626b0eda06671b4cbbc4cdd1344440c&stat=instructions:u

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

Changes

Address review comment #128466 (comment)

---

Full diff: https://github.com/llvm/llvm-project/pull/128695.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp (+2-1)
• (modified) llvm/test/Transforms/InstCombine/load.ll (+30)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 622884ea1eb46..221511e9aba0b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -996,7 +996,8 @@ Value *InstCombinerImpl::simplifyNonNullOperand(Value *V,
   if (!V->hasOneUse())
     return nullptr;
 
-  if (Depth == 1)
+  constexpr unsigned RecursionLimit = 3;
+  if (Depth == RecursionLimit)
     return nullptr;
 
   if (auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll
index a5ad1e0c21526..99185a4e6f043 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -451,3 +451,33 @@ define i32 @load_select_with_null_gep(i1 %cond, ptr %p, i64 %off) {
   %res = load i32, ptr %gep, align 4
   ret i32 %res
 }
+
+define i16 @load_select_with_null_gep2(i1 %cond, ptr %p, i64 %x) {
+; CHECK-LABEL: @load_select_with_null_gep2(
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL:%.*]], i64 -2
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP]], align 2
+; CHECK-NEXT:    ret i16 [[RES]]
+;
+  %sel = select i1 %cond, ptr %p, ptr null
+  %invariant.gep = getelementptr i8, ptr %sel, i64 -2
+  %gep = getelementptr i16, ptr %invariant.gep, i64 %x
+  %res = load i16, ptr %gep, align 2
+  ret i16 %res
+}
+
+define i16 @load_select_with_null_ge3(i1 %cond, ptr %p, i64 %x, i64 %y) {
+; CHECK-LABEL: @load_select_with_null_ge3(
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL:%.*]], i64 -2
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i16, ptr [[GEP]], i64 [[Y:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP2]], align 2
+; CHECK-NEXT:    ret i16 [[RES]]
+;
+  %sel = select i1 %cond, ptr %p, ptr null
+  %invariant.gep = getelementptr i8, ptr %sel, i64 -2
+  %gep = getelementptr i16, ptr %invariant.gep, i64 %x
+  %gep2 = getelementptr i16, ptr %gep, i64 %y
+  %res = load i16, ptr %gep2, align 2
+  ret i16 %res
+}

[nikic]

LGTM