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Re: [PATCH] Fix bug in simplify_ternary_operation

On 08/28/2017 08:26 PM, Tom de Vries wrote:

I think I found a bug in r17465:
       * cse.c (simplify_ternary_operation): Handle more IF_THEN_ELSE

diff --git a/gcc/cse.c b/gcc/cse.c
index e001597..3c27387 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -4713,6 +4713,17 @@ simplify_ternary_operation (code, mode, op0_mode, op0, op1, op2)

Note: the parameters of simplify_ternary_operation have the following meaning:
/* Simplify CODE, an operation with result mode MODE and three operands,
    OP0, OP1, and OP2.  OP0_MODE was the mode of OP0 before it became
    a constant.  Return 0 if no simplifications is possible.  */

simplify_ternary_operation (code, mode, op0_mode, op0, op1, op2)
      enum rtx_code code;
      enum machine_mode mode, op0_mode;
      rtx op0, op1, op2;

          && rtx_equal_p (XEXP (op0, 1), op1)
          && rtx_equal_p (XEXP (op0, 0), op2))
        return op2;
+      else if (! side_effects_p (op0))
+       {
+         rtx temp;
+         temp = simplify_relational_operation (GET_CODE (op0), op0_mode,
+ XEXP (op0, 0), XEXP (op0, 1));

We're handling code == IF_THEN_ELSE here, so op0 is the condition, op1 is the 'then expr' and op2 is the 'else expr'.

The parameters of simplify_relational_operation have the following meaning:
/* Like simplify_binary_operation except used for relational operators.
    MODE is the mode of the operands, not that of the result.  If MODE
    is VOIDmode, both operands must also be VOIDmode and we compare the
    operands in "infinite precision".

    If no simplification is possible, this function returns zero.
    Otherwise, it returns either const_true_rtx or const0_rtx.  */

simplify_relational_operation (code, mode, op0, op1)
      enum rtx_code code;
      enum machine_mode mode;
      rtx op0, op1;

The problem in the patch is that we use op0_mode argument for the mode parameter. The mode parameter of simplify_relational_operation needs to be the mode of the operands of the condition, while op0_mode is the mode of the condition.

Patch below fixes this on current trunk.

[ I found this by running into an ICE in gcc.c-torture/compile/pr28776-2.c for gcn target. I haven't been able to reproduce this with an upstream branch yet. ]

Filed as PR82020 - "ICE in decompose at rtl.h:2126" ( ).

OK for trunk if bootstrap and reg-test for x86_64 succeeds?

bootstrap and reg-test for x86_64 done, no issues found.

- Tom

[ reposting patch with ChangeLog entry ]
Fix comparison mode in simplify_ternary_operation

2017-08-29  Tom de Vries  <>

	PR rtl-optimization/82020
	* simplify-rtx.c (simplify_ternary_operation): Fix comparison mode of
	IF_THEN_ELSE condition.

 gcc/simplify-rtx.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 0133d43..fbf979b 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -5567,8 +5567,6 @@ simplify_ternary_operation (enum rtx_code code, machine_mode mode,
 					      XEXP (op0, 0), XEXP (op0, 1));
-	  if (cmp_mode == VOIDmode)
-	    cmp_mode = op0_mode;
 	  temp = simplify_relational_operation (GET_CODE (op0), op0_mode,
 			  			cmp_mode, XEXP (op0, 0),
 						XEXP (op0, 1));

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