https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113787
Bug ID: 113787 Summary: [14 Regression] Wrong code at -O with ipa-modref on aarch64 Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: acoplan at gcc dot gnu.org Target Milestone: --- The following testcase appears to be miscompiled on the trunk, on aarch64-linux-gnu: $ cat t.c void foo(int x, int y, int z, int d, int *buf) { for(int i = z; i < y-z; ++i) for(int j = 0; j < d; ++j) /* buf[x(i+1) + j] = buf[x(i+1)-j-1] */ buf[i*x+(x-z+j)] = buf[i*x+(x-z-1-j)]; } void bar(int x, int y, int z, int d, int *buf) { for(int i = 0; i < d; ++i) for(int j = z; j < x-z; ++j) /* buf[j+(y+i)*x] = buf[j+(y-1-i)*x] */ buf[j+(y-z+i)*x] = buf[j+(y-z-1-i)*x]; } __attribute__((noipa)) void baz(int x, int y, int d, int *buf) { foo(x, y, 0, d, buf); bar(x, y, 0, d, buf); } int main(void) { int a[] = { 1, 2, 3 }; baz (1, 2, 1, a); /* foo does: buf[1] = buf[0]; buf[2] = buf[1]; bar does: buf[2] = buf[1]; (no-op) so we should have { 1, 1, 1 }. */ for (int i = 0; i < 3; i++) if (a[i] != 1) __builtin_abort (); } $ gcc t.c -O -fno-ipa-modref $ ./a.out $ gcc t.c -O $ ./a.out Aborted The problem seems to be that the call to foo gets incorrectly optimized out from baz when ipa-modref is enabled: $ gcc -c -S -o /dev/null t.c -O -fno-ipa-modref -fdump-tree-optimized=good.tree $ gcc -c -S -o /dev/null t.c -O -fdump-tree-optimized=bad.tree $ diff -u good.tree bad.tree --- good.tree 2024-02-06 13:23:36.080926703 +0000 +++ bad.tree 2024-02-06 13:23:38.356916302 +0000 @@ -223,7 +223,6 @@ void baz (int x, int y, int d, int * buf) { <bb 2> [local count: 1073741824]: - foo (x_2(D), y_3(D), 0, d_4(D), buf_5(D)); bar (x_2(D), y_3(D), 0, d_4(D), buf_5(D)); return; I can't seem to reproduce the issue with GCC 13 or on x86_64.