1228becf7d
This patch deduces `noundef` attributes for return values. IIUC, a function returns `noundef` values iff all of its return values are guaranteed not to be `undef` or `poison`. Definition of `noundef` from LangRef: ``` noundef This attribute applies to parameters and return values. If the value representation contains any undefined or poison bits, the behavior is undefined. Note that this does not refer to padding introduced by the type’s storage representation. ``` Alive2: https://alive2.llvm.org/ce/z/g8Eis6 Compile-time impact: http://llvm-compile-time-tracker.com/compare.php?from=30dcc33c4ea3ab50397a7adbe85fe977d4a400bd&to=c5e8738d4bfbf1e97e3f455fded90b791f223d74&stat=instructions:u |stage1-O3|stage1-ReleaseThinLTO|stage1-ReleaseLTO-g|stage1-O0-g|stage2-O3|stage2-O0-g|stage2-clang| |--|--|--|--|--|--|--| |+0.01%|+0.01%|-0.01%|+0.01%|+0.03%|-0.04%|+0.01%| The motivation of this patch is to reduce the number of `freeze` insts and enable more optimizations.
43 lines
1.2 KiB
LLVM
43 lines
1.2 KiB
LLVM
; RUN: opt -passes=function-attrs -S < %s | FileCheck %s
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; This checks for a previously existing iterator wraparound bug in
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; FunctionAttrs, and in the process covers corner cases with varargs.
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declare void @llvm.va_start(ptr)
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declare void @llvm.va_end(ptr)
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define void @va_func(ptr readonly %b, ...) readonly nounwind {
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; CHECK-LABEL: define void @va_func(ptr nocapture readonly %b, ...)
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entry:
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%valist = alloca i8
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call void @llvm.va_start(ptr %valist)
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call void @llvm.va_end(ptr %valist)
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%x = call i32 @caller(ptr %b)
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ret void
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}
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define i32 @caller(ptr %x) {
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; CHECK-LABEL: define noundef i32 @caller(ptr nocapture readonly %x)
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entry:
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call void(ptr,...) @va_func(ptr null, i32 0, i32 0, i32 0, ptr %x)
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ret i32 42
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}
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define void @va_func2(ptr readonly %b, ...) {
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; CHECK-LABEL: define void @va_func2(ptr nocapture readonly %b, ...)
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entry:
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%valist = alloca i8
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call void @llvm.va_start(ptr %valist)
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call void @llvm.va_end(ptr %valist)
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%x = call i32 @caller(ptr %b)
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ret void
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}
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define i32 @caller2(ptr %x, ptr %y) {
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; CHECK-LABEL: define noundef i32 @caller2(ptr nocapture readonly %x, ptr %y)
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entry:
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call void(ptr,...) @va_func2(ptr %x, i32 0, i32 0, i32 0, ptr %y)
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ret i32 42
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}
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