50b2a113db
As a result of -ftrivial-auto-var-init, clang generates instructions to
set alloca'd memory to a given pattern, right after the allocation site.
In some cases, this (somehow costly) operation could be delayed, leading
to conditional execution in some cases.
This is not an uncommon situation: it happens ~500 times on the cPython
code base, and much more on the LLVM codebase. The benefit greatly
varies on the execution path, but it should not regress on performance.
This is a recommit of cca01008cc with
MemorySSA update fixes.
Differential Revision: https://reviews.llvm.org/D137707
71 lines
2.3 KiB
LLVM
71 lines
2.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -S -passes='move-auto-init' -verify-memoryssa | FileCheck %s
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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; In that case, the store to %val happens before the fence and cannot go past
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; it.
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define void @foo(i32 %x) {
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; CHECK-LABEL: @foo(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[VAL:%.*]] = alloca i32, align 4
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; CHECK-NEXT: store i32 -1431655766, ptr [[VAL]], align 4, !annotation !0
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; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne i32 [[X:%.*]], 0
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; CHECK-NEXT: fence acquire
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; CHECK-NEXT: br i1 [[TOBOOL]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
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; CHECK: if.then:
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; CHECK-NEXT: call void @dump(ptr [[VAL]])
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; CHECK-NEXT: br label [[IF_END]]
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; CHECK: if.end:
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; CHECK-NEXT: ret void
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;
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entry:
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%val = alloca i32, align 4
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store i32 -1431655766, ptr %val, align 4, !annotation !0
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%tobool = icmp ne i32 %x, 0
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fence acquire
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br i1 %tobool, label %if.then, label %if.end
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if.then: ; preds = %entry
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call void @dump(ptr %val)
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br label %if.end
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if.end: ; preds = %if.then, %entry
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ret void
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}
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; In that case, the store to %val happens after the fence and it is moved within
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; the true branch as expected.
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define void @bar(i32 %x) {
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; CHECK-LABEL: @bar(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[VAL:%.*]] = alloca i32, align 4
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; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne i32 [[X:%.*]], 0
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; CHECK-NEXT: fence acquire
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; CHECK-NEXT: br i1 [[TOBOOL]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
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; CHECK: if.then:
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; CHECK-NEXT: store i32 -1431655766, ptr [[VAL]], align 4, !annotation !0
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; CHECK-NEXT: call void @dump(ptr [[VAL]])
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; CHECK-NEXT: br label [[IF_END]]
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; CHECK: if.end:
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; CHECK-NEXT: ret void
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;
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entry:
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%val = alloca i32, align 4
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%tobool = icmp ne i32 %x, 0
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fence acquire
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store i32 -1431655766, ptr %val, align 4, !annotation !0
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br i1 %tobool, label %if.then, label %if.end
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if.then: ; preds = %entry
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call void @dump(ptr %val)
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br label %if.end
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if.end: ; preds = %if.then, %entry
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ret void
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}
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declare void @dump(ptr)
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!0 = !{!"auto-init"}
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