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[PATCH][ARM] Restrict {load,store}_multiple expanders to MAX_LD_STM_OPS regs


Hi all,

The load/store-multiple expanders reject a number of registers outside of [2-14]
but the arm_gen_{load,store}_multiple functions that they called down to have an even
stricter restriction of <= MAX_LDM_STM_OPS that is <= 4. If load_multiple was called with
a number of regs larger than 4 the assert would trigger and we'd ICE.
This patch fixes that possibility by FAILing in expansion if the number of requested
regs is > MAX_LDM_STM_OPS.

The reason we never hit this currently is that the load,store_multiple standard names are
only used in a single place in expr.c to load the argument registers from to a function call.
By a happy coincidence for arm the number of argument registers is 4 so we never exceed that.
The arm backend never calls the load,store_multiple expanders directly but rather the
arm_gen* functions and it makes sure that they're never called with anything
 > MAX_LDM_STM_OPS.

I hit this issue only due to a buggy change I made to expr.c that ended up requesting a
load_multiple of 5 registers which the expander should have rejected but it didn't,
causing an ICE.

If we add more uses of load/store_multiple in the midend this issue will be a loaded gun.

Bootstrapped and tested on arm-none-linux-gnueabihf.

Ok for trunk?

Thanks,
Kyrill

2015-04-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * config/arm/arm.md (load_multiple): Reject operand 2 greater than
    MAX_LDM_STM_OPS.
    (store_multiple): Likewise.
commit dbfb3478c8c15ff38156122ed0a827829cf8c095
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Wed Mar 18 11:17:48 2015 +0000

    [ARM] Restrict {load,store}_multiple expanders to MAX_LD_STM_OPS regs

diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index abe2b4c..dcc4446 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -6775,7 +6775,7 @@ (define_expand "load_multiple"
 
   /* Support only fixed point registers.  */
   if (!CONST_INT_P (operands[2])
-      || INTVAL (operands[2]) > 14
+      || INTVAL (operands[2]) > MAX_LDM_STM_OPS
       || INTVAL (operands[2]) < 2
       || !MEM_P (operands[1])
       || !REG_P (operands[0])
@@ -6800,7 +6800,7 @@ (define_expand "store_multiple"
 
   /* Support only fixed point registers.  */
   if (!CONST_INT_P (operands[2])
-      || INTVAL (operands[2]) > 14
+      || INTVAL (operands[2]) > MAX_LDM_STM_OPS
       || INTVAL (operands[2]) < 2
       || !REG_P (operands[1])
       || !MEM_P (operands[0])

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