72c243017d
This patch addresses PR middle-end/98420, which is inappropriate constant folding of x - x to 0.0 (in match.pd) when -frounding-math is specified. Specifically, x - x may be -0.0 with FE_DOWNWARD as the rounding mode. To summarize, the desired IEEE behaviour, x - x for floating point x, (1) can't be folded to 0.0 by default, due to the possibility of NaN or Inf (2) can be folded to 0.0 with -ffinite-math-only (3) can't be folded to 0.0 with -ffinite-math-only -frounding-math (4) can be folded with -ffinite-math-only -frounding-math -fno-signed-zeros 2022-03-12 Roger Sayle <roger@nextmovesoftware.com> gcc/ChangeLog PR middle-end/98420 * match.pd (minus @0 @0): Additional checks for -fno-rounding-math (the defaut) or -fno-signed-zeros. gcc/testsuite/ChangeLog PR middle-end/98420 * gcc.dg/pr98420.c: New test case. |
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