50d10b5c1c
This patch adds a new __builtin_assume_dereferenceable to encode
dereferenceability of a pointer using llvm.assume with an operand
bundle.
For now the builtin only accepts constant sizes, I am planning to drop
this restriction in a follow-up change.
This can be used to better optimize cases where a pointer is known to be
dereferenceable, e.g. unconditionally loading from p2 when vectorizing
the loop.
int *get_ptr();
void foo(int* src, int x) {
int *p2 = get_ptr();
__builtin_assume_aligned(p2, 4);
__builtin_assume_dereferenceable(p2, 4000);
for (unsigned I = 0; I != 1000; ++I) {
int x = src[I];
if (x == 0)
x = p2[I];
src[I] = x;
}
}
PR: https://github.com/llvm/llvm-project/pull/121789
35 lines
1.5 KiB
C
35 lines
1.5 KiB
C
// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
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// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
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// CHECK-LABEL: @test1(
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[A_ADDR:%.*]] = alloca ptr, align 8
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// CHECK-NEXT: store ptr [[A:%.*]], ptr [[A_ADDR]], align 8
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// CHECK-NEXT: [[TMP0:%.*]] = load ptr, ptr [[A_ADDR]], align 8
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// CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0]], i64 10) ]
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// CHECK-NEXT: [[TMP1:%.*]] = load ptr, ptr [[A_ADDR]], align 8
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// CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[TMP1]], i64 0
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// CHECK-NEXT: [[TMP2:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
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// CHECK-NEXT: ret i32 [[TMP2]]
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//
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int test1(int *a) {
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__builtin_assume_dereferenceable(a, 10);
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return a[0];
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}
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// CHECK-LABEL: @test2(
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[A_ADDR:%.*]] = alloca ptr, align 8
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// CHECK-NEXT: store ptr [[A:%.*]], ptr [[A_ADDR]], align 8
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// CHECK-NEXT: [[TMP0:%.*]] = load ptr, ptr [[A_ADDR]], align 8
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// CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0]], i64 32) ]
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// CHECK-NEXT: [[TMP1:%.*]] = load ptr, ptr [[A_ADDR]], align 8
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// CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[TMP1]], i64 0
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// CHECK-NEXT: [[TMP2:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
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// CHECK-NEXT: ret i32 [[TMP2]]
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//
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int test2(int *a) {
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__builtin_assume_dereferenceable(a, 32ull);
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return a[0];
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}
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