https://bugs.llvm.org/show_bug.cgi?id=39170
Bug ID: 39170
Summary: [AArch64] redundant adrp/ldr on aarch64 (GCC does
better)
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: k...@google.com
CC: llvm-bugs@lists.llvm.org
clang version 8.0.0 (trunk 343550)
typedef struct {
long a, b;
} S;
void foo(S *s) {
s->a = 1;
s->b = 0;
}
clang++ -fomit-frame-pointer -O3 -S -o - store16.c -target aarch64-linux
adrp x8, .LCPI0_0 <<<<<<<<<<<<
ldr q0, [x8, :lo12:.LCPI0_0] <<<<<<<<<<<<
str q0, [x0]
ret
While gcc 6.3 does this (much nicer!!):
mov x1, 1
stp x1, xzr, [x0]
ret
If I change "s->b = 0" to "s->b = 1" clang generates the same code
(loads the constant)
but gcc keeps avoiding loads (still better!!)
mov x2, 1
mov x1, 2
stp x2, x1, [x0]
ret
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