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This intrinsic takes two arguments, ``%ptr`` and ``%offset``. It loads a 32-bit value from the address ``%ptr + %offset``, adds ``%ptr`` to that value and returns it. The constant folder specifically recognizes the form of this intrinsic and the constant initializers it may load from; if a loaded constant initializer is known to have the form ``i32 trunc(x - %ptr)``, the intrinsic call is folded to ``x``. LLVM provides that the calculation of such a constant initializer will not overflow at link time under the medium code model if ``x`` is an ``unnamed_addr`` function. However, it does not provide this guarantee for a constant initializer folded into a function body. This intrinsic can be used to avoid the possibility of overflows when loading from such a constant. Differential Revision: http://reviews.llvm.org/D18367 llvm-svn: 267223
27 lines
1023 B
LLVM
27 lines
1023 B
LLVM
; RUN: opt -pre-isel-intrinsic-lowering -S -o - %s | FileCheck %s
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; CHECK: define i8* @foo32(i8* [[P:%.*]], i32 [[O:%.*]])
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define i8* @foo32(i8* %p, i32 %o) {
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; CHECK: [[OP:%.*]] = getelementptr i8, i8* [[P]], i32 [[O]]
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; CHECK: [[OPI32:%.*]] = bitcast i8* [[OP]] to i32*
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; CHECK: [[OI32:%.*]] = load i32, i32* [[OPI32]], align 4
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; CHECK: [[R:%.*]] = getelementptr i8, i8* [[P]], i32 [[OI32]]
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; CHECK: ret i8* [[R]]
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%l = call i8* @llvm.load.relative.i32(i8* %p, i32 %o)
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ret i8* %l
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}
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; CHECK: define i8* @foo64(i8* [[P:%.*]], i64 [[O:%.*]])
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define i8* @foo64(i8* %p, i64 %o) {
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; CHECK: [[OP:%.*]] = getelementptr i8, i8* [[P]], i64 [[O]]
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; CHECK: [[OPI32:%.*]] = bitcast i8* [[OP]] to i32*
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; CHECK: [[OI32:%.*]] = load i32, i32* [[OPI32]], align 4
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; CHECK: [[R:%.*]] = getelementptr i8, i8* [[P]], i32 [[OI32]]
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; CHECK: ret i8* [[R]]
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%l = call i8* @llvm.load.relative.i64(i8* %p, i64 %o)
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ret i8* %l
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}
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declare i8* @llvm.load.relative.i32(i8*, i32)
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declare i8* @llvm.load.relative.i64(i8*, i64)
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