Reproducer: #include <stdio.h> unsigned long long int var_0 = 18128133247277979402ULL; long long int var_14 = 6557021550272328915LL; unsigned long long int var_83 = 10966786425750692026ULL; void test() { var_14 = var_0 + (bool)7; var_83 = 1 + (int)var_0; // 1 + 888395530 } int main() { test(); printf("%llu\n", var_83); } https://godbolt.org/z/axYx1f >$ g++ -O0 driver.cpp && ./a.out 888395531 >$ g++ -O1 driver.cpp && ./a.out 18128133247277979403 gcc version 11.0.0 20210112 (cf2ac1c30af0fa783c8d72e527904dda5d8cc330)
Thanks for the report, started with r10-2711-g3ed01d5408045d80.
I will have a look.
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>: https://gcc.gnu.org/g:ffd28c265e6d611983cd27e9332dc799039a3f04 commit r11-6632-gffd28c265e6d611983cd27e9332dc799039a3f04 Author: Richard Biener <rguenther@suse.de> Date: Wed Jan 13 09:43:52 2021 +0100 tree-optimization/98640 - fix bogus sign-extension with VN VN tried to express a sign extension from int to long of a trucated quantity with a plain conversion but that loses the truncation. Since there's no single operand doing truncate plus sign extend (there was a proposed SEXT_EXPR to do that at some point mapping to RTL sign_extract) don't bother to appropriately model this with two ops (which the VN insert machinery doesn't handle and which is unlikely to CSE fully). 2021-01-13 Richard Biener <rguenther@suse.de> PR tree-optimization/98640 * tree-ssa-sccvn.c (visit_nary_op): Do not try to handle plus or minus from a truncated operand to be sign-extended. * gcc.dg/torture/pr98640.c: New testcase.
The releases/gcc-10 branch has been updated by Richard Biener <rguenth@gcc.gnu.org>: https://gcc.gnu.org/g:268b54382e5248ee1a5e3f4a0841358e03290d17 commit r10-9407-g268b54382e5248ee1a5e3f4a0841358e03290d17 Author: Richard Biener <rguenther@suse.de> Date: Wed Jan 13 09:43:52 2021 +0100 tree-optimization/98640 - fix bogus sign-extension with VN VN tried to express a sign extension from int to long of a trucated quantity with a plain conversion but that loses the truncation. Since there's no single operand doing truncate plus sign extend (there was a proposed SEXT_EXPR to do that at some point mapping to RTL sign_extract) don't bother to appropriately model this with two ops (which the VN insert machinery doesn't handle and which is unlikely to CSE fully). 2021-01-13 Richard Biener <rguenther@suse.de> PR tree-optimization/98640 * tree-ssa-sccvn.c (visit_nary_op): Do not try to handle plus or minus from a truncated operand to be sign-extended. * gcc.dg/torture/pr98640.c: New testcase. (cherry picked from commit ffd28c265e6d611983cd27e9332dc799039a3f04)
Fixed.