[llvm] [SROA] Optimize reloaded values in allocas that escape into readonly nocapture calls. (PR #116645)

[Nikita Popov via llvm-commits]

================
@@ -0,0 +1,309 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=sroa -S | FileCheck %s
+
+declare void @callee(ptr nocapture readonly %p)
+
+define i32 @simple() {
+; CHECK-LABEL: @simple(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i32 0, ptr [[A]], align 4
+; CHECK-NEXT:    call void @callee(ptr [[A]])
+; CHECK-NEXT:    ret i32 0
+;
+  %a = alloca i32
+  store i32 0, ptr %a
+  call void @callee(ptr %a)
+  %l1 = load i32, ptr %a
+  ret i32 %l1
+}
+
+define i32 @smallbig() {
+; CHECK-LABEL: @smallbig(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i8 0, ptr [[A]], align 1
+; CHECK-NEXT:    call void @callee(ptr [[A]])
+; CHECK-NEXT:    [[L1:%.*]] = load i32, ptr [[A]], align 4
+; CHECK-NEXT:    ret i32 [[L1]]
+;
+  %a = alloca i32
+  store i8 0, ptr %a
+  call void @callee(ptr %a)
+  %l1 = load i32, ptr %a
+  ret i32 %l1
+}
+
+define i32 @twoalloc() {
+; CHECK-LABEL: @twoalloc(
+; CHECK-NEXT:    [[A:%.*]] = alloca { i32, i32 }, align 8
+; CHECK-NEXT:    store i32 0, ptr [[A]], align 4
+; CHECK-NEXT:    [[B:%.*]] = getelementptr i32, ptr [[A]], i32 1
+; CHECK-NEXT:    store i32 1, ptr [[B]], align 4
+; CHECK-NEXT:    call void @callee(ptr [[A]])
+; CHECK-NEXT:    ret i32 1
+;
+  %a = alloca {i32, i32}
+  store i32 0, ptr %a
+  %b = getelementptr i32, ptr %a, i32 1
+  store i32 1, ptr %b
+  call void @callee(ptr %a)
+  %l1 = load i32, ptr %a
+  %l2 = load i32, ptr %b
----------------
nikic wrote:

Use both %l1 and %l2 here?

https://github.com/llvm/llvm-project/pull/116645