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  1. RHEL
  2. RHEL-76359

gcc: With -frounding-math, gcc-11.5.0-3.el9 miscompiles struct initializers for floats

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    • rhel-9.6
    • rhel-9.6
    • gcc
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    • rhel-pt-gcc
    • ssg_platform_tools
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    • Red Hat Enterprise Linux
    • PT GCC 2025 S01
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      Reproducer:

      typedef struct
{
  float x;
} S;
S s = { 3.3 };

      Without -frounding-math:

              .globl  s
        .data
        .align 4
        .type   s, @object
        .size   s, 4
s:
        .long   1079194419
        .ident  "GCC: (GNU) 11.5.0 20240719 (Red Hat 11.5.0-3)"

      With -frounding-math:

              .globl  s
        .data
        .align 4
        .type   s, @object
        .size   s, 4
s:
        .long   1717986918
        .long   1074423398
        .ident  "GCC: (GNU) 11.5.0 20240719 (Red Hat 11.5.0-3)"

      Note that the struct size did not change, but GCC seems to emit the constant as double.

      Original spotted by skolosov@redhat.com while looking at glibc-2.34-159.el9 failures. I tracked it down from the localedata/tst_swscanf crash: due to the incorrect initializer layout, the test is not able to find the sentinel value that terminates the test case list.

              rhn-support-vkadlcik Vaclav Kadlcik
              fweimer@redhat.com Florian Weimer
              Marek Polacek Marek Polacek
              Vaclav Kadlcik Vaclav Kadlcik
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                Created:
                Updated:
                Resolved: