Fix non-determinism in bootstrap gcc #22
Description
I've been noticing that the binary bootstrap gcc has differed on each build. At first, I thought it might be because of the parallelism, but even with ZB_BUILD_CORES=1, the bootstrap produces differing results. I compared two runs:
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/lib/libstdc++.a and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/lib/libstdc++.a differ
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/lib/libstdc++.la and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/lib/libstdc++.la differ
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/lib/libsupc++.a and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/lib/libsupc++.a differ
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/lib/libsupc++.la and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/lib/libsupc++.la differ
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/libexec/gcc/x86_64-unknown-linux-musl/4.2.1/cc1 and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/libexec/gcc/x86_64-unknown-linux-musl/4.2.1/cc1 differ
Files /opt/zb/store/6ssl5z26zmr9dn2iz4xi17a13ia7qz8y-gcc-4.2.1/libexec/gcc/x86_64-unknown-linux-musl/4.2.1/cc1plus and /opt/zb/store/z3bi28c5p48vszan6ks1sga8vw41zcyz-gcc-4.2.1/libexec/gcc/x86_64-unknown-linux-musl/4.2.1/cc1plus differ
The .la files are a bit of a red herring, since they are self-references.
Difference in cc1:
--- /proc/self/fd/16 2025-05-07 19:23:05.018537811 -0700
+++ /proc/self/fd/23 2025-05-07 19:23:05.018537811 -0700
@@ -286762,7 +286762,7 @@
00460290: 0000 0000 0000 0000 0000 0000 0000 0000 ................
004602a0: 635f 6669 6e69 7368 5f6f 6d70 5f61 746f c_finish_omp_ato
004602b0: 6d69 6300 0000 0000 0000 0000 0000 0000 mic.............
-004602c0: 54c3 ed4c 6447 9662 9fc6 98c0 c492 9b5a T..LdG.b.......Z
+004602c0: dd8b 1bbe 63f0 2685 ccae 48ae 53cb 6394 ....c.&...H.S.c.
004602d0: 2548 7769 6c6c 206e 6576 6572 2062 6520 %Hwill never be
004602e0: 6578 6563 7574 6564 002e 2e2f 2e2e 2f73 executed.../../s
004602f0: 7263 5f67 6363 2f67 6363 2f74 7265 652d rc_gcc/gcc/tree-Difference in cc1plus:
--- /proc/self/fd/16 2025-05-07 19:23:51.220552986 -0700
+++ /proc/self/fd/23 2025-05-07 19:23:51.220552986 -0700
@@ -318664,7 +318664,7 @@
004dcc70: 6573 7469 6d61 7465 5f6e 756d 5f69 6e73 estimate_num_ins
004dcc80: 6e73 5f31 0063 6f70 795f 626f 6479 5f72 ns_1.copy_body_r
004dcc90: 0000 0000 0000 0000 0000 0000 0000 0000 ................
-004dcca0: 11b6 3c5d ed58 abfc bad8 5481 512a 2b7a ..<].X....T.Q*+z
+004dcca0: 7363 c36c f4d8 8aa4 dd9f a936 049c 9f7a sc.l.......6...z
004dccb0: 2548 7769 6c6c 206e 6576 6572 2062 6520 %Hwill never be
004dccc0: 6578 6563 7574 6564 002e 2e2f 2e2e 2f73 executed.../../s
004dccd0: 7263 5f67 6363 2f67 6363 2f74 7265 652d rc_gcc/gcc/tree-The differences in the .a files are more extensive, but seem not reference-related. libsupc++.a is a smaller difference, so included here:
--- /proc/self/fd/16 2025-05-07 19:25:18.568187440 -0700
+++ /proc/self/fd/23 2025-05-07 19:25:18.568187440 -0700
@@ -1379,7 +1379,7 @@
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@@ -1673,7 +1673,7 @@
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-0000c5f0: 5f30 3030 3030 3030 305f 4544 3135 3032 _00000000_ED1502
-0000c600: 3034 3130 6765 745f 676c 6f62 616c 4576 0410get_globalEv
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0000c630: 002e 6e6f 7465 2e47 4e55 2d73 7461 636b ..note.GNU-stack
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@@ -5390,7 +5390,7 @@
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-00015100: 3030 5f33 4445 3338 3042 4131 3667 6574 00_3DE380BA16get
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000315f0: 7874 2e5f 5f63 7861 5f76 6563 5f63 6c65 xt.__cxa_vec_cle(The libstdc++.a diff is similar but is 10x larger.)