a874d63344
After the recent discussion on cfe-dev 'Can indirect class parameters be noalias?' [1], it seems like using using noalias is problematic for current C++, but should be allowed for C-only code. This patch introduces a new option to let the user indicate that it is safe to mark indirect class parameters as noalias. Note that this also applies to external callers, e.g. it might not be safe to use this flag for C functions that are called by C++ functions. In targets that allocate indirect arguments in the called function, this enables more agressive optimizations with respect to memory operations and brings a ~1% - 2% codesize reduction for some programs. [1] : http://lists.llvm.org/pipermail/cfe-dev/2020-July/066353.html Reviewed By: rjmccall Differential Revision: https://reviews.llvm.org/D85473
17 lines
580 B
C
17 lines
580 B
C
// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
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// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
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// A struct large enough so it is not passed in registers on ARM64.
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struct Foo {
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int a;
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int b;
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int c;
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int d;
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int e;
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int f;
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};
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// WITH_NOALIAS: define void @take(%struct.Foo* noalias %arg)
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// NO_NOALIAS: define void @take(%struct.Foo* %arg)
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void take(struct Foo arg) {}
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