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b330f79c8f
Enable value forwarding for loads from `calloc()` without an intervening
store.
This change extends GVN to handle the following case:
%1 = tail call noalias i8* @calloc(i64 1, i64 4)
%2 = bitcast i8* %1 to i32*
; This load is trivially constant zero
%3 = load i32* %2, align 4
This is analogous to the handling for `malloc()` in the same places.
`malloc()` returns `undef`; `calloc()` returns a zero value. Note that
it is correct to return zero even for out of bounds GEPs since the
result of such a GEP would be undefined.
Patch by Philip Reames!
llvm-svn: 210828
26 lines
825 B
LLVM
26 lines
825 B
LLVM
; RUN: opt -S -basicaa -gvn < %s | FileCheck %s
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; RUN: opt -S -basicaa -gvn -disable-simplify-libcalls < %s | FileCheck %s -check-prefix=CHECK_NO_LIBCALLS
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; Check that loads from calloc are recognized as being zero.
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
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; Function Attrs: nounwind uwtable
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define i32 @test1() {
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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%2 = bitcast i8* %1 to i32*
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; This load is trivially constant zero
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%3 = load i32* %2, align 4
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ret i32 %3
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; CHECK-LABEL: @test1(
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; CHECK-NOT: %3 = load i32* %2, align 4
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; CHECK: ret i32 0
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; CHECK_NO_LIBCALLS-LABEL: @test1(
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; CHECK_NO_LIBCALLS: load
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; CHECK_NO_LIBCALLS: ret i32 %
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}
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declare noalias i8* @calloc(i64, i64)
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