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Fix PR 93044: extra cast is not removed

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In this case we are not removing convert to a bigger size
back to the same size (or smaller) if signedness does not
match.
For an example:
```
  signed char _1;
...
  _1 = *a_4(D);
  b_5 = (short unsigned int) _1;
  _2 = (unsigned char) b_5;
```
The inner cast is not needed and can be removed but was not.
The match pattern for removing the extra cast is overly
complex so decided to add a new case for rather than trying
to modify the current if statement here.

Committed as approved. Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR tree-optimization/93044
	* match.pd (nested int casts): A truncation (to the same size or smaller)
	can always remove the inner cast.

gcc/testsuite/ChangeLog:

	PR tree-optimization/93044
	* gcc.dg/tree-ssa/cast-1.c: New test.
	* gcc.dg/tree-ssa/cast-2.c: New test.
This commit is contained in:
Andrew Pinski
2023-07-23 21:44:39 +00:00
parent a349ba16f1
commit cc2003cd87
3 changed files with 34 additions and 0 deletions
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10
gcc/match.pd
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@@ -4340,6 +4340,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& ! (final_ptr && inside_prec != inter_prec))
(ocvt @0))
/* `(outer:M)(inter:N) a:O`
can be converted to `(outer:M) a`
if M <= O && N >= O. No matter what signedness of the casts,
as the final is either a truncation from the original or just
a sign change of the type. */
(if (inside_int && inter_int && final_int
&& final_prec <= inside_prec
&& inter_prec >= inside_prec)
(convert @0))
/* A truncation to an unsigned type (a zero-extension) should be
canonicalized as bitwise and of a mask. */
(if (GIMPLE /* PR70366: doing this in GENERIC breaks -Wconversion. */

12
gcc/testsuite/gcc.dg/tree-ssa/cast-1.c Normal file
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@@ -0,0 +1,12 @@
/* { dg-do compile } */
/* { dg-options "-O1 -fdump-tree-optimized" } */
void f(signed char *a, unsigned char *c)
{
unsigned short b = *a;
*c = ((unsigned char)b);
}
/* { dg-final { scan-tree-dump-not "\\(short unsigned int\\)" "optimized"} } */

12
gcc/testsuite/gcc.dg/tree-ssa/cast-2.c Normal file
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@@ -0,0 +1,12 @@
/* { dg-do compile } */
/* { dg-options "-O1 -fdump-tree-optimized" } */
void f(signed short *a, unsigned char *c)
{
unsigned long b = *a;
*c = ((unsigned char)b);
}
/* { dg-final { scan-tree-dump-not "\\(long unsigned int\\)" "optimized"} } */