early-remat: Handle sets of multiple candidate regs [PR94605]

early-remat.c:process_block wasn't handling insns that set multiple
candidate registers, which led to an assertion failure at the end
of the main loop.

Instructions that set two pseudos aren't rematerialisation candidates in
themselves, but we still need to track them if another instruction that
sets the same register is a rematerialisation candidate.

2020-04-16  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR rtl-optimization/94605
	* early-remat.c (early_remat::process_block): Handle insns that
	set multiple candidate registers.

gcc/testsuite/
	PR rtl-optimization/94605
	* gcc.target/aarch64/sve/pr94605.c: New test.

gcc/ChangeLog

+2020-04-16  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR rtl-optimization/94605
+	* early-remat.c (early_remat::process_block): Handle insns that
+	set multiple candidate registers.
+
 2020-04-16  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/94614

gcc/early-remat.c

@@ -2020,7 +2020,7 @@ early_remat::process_block (basic_block bb)
 	}
 
       /* Now process definitions.  */
-      if (next_def && insn == next_def->insn)
+      while (next_def && insn == next_def->insn)
 	{
 	  unsigned int gen = canon_candidate (next_candidate);
 

gcc/testsuite/ChangeLog

+2020-04-16  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR rtl-optimization/94605
+	* gcc.target/aarch64/sve/pr94605.c: New test.
+
 2020-04-16  Richard Biener  <rguenther@suse.de>
 
 	* gcc.dg/graphite/interchange-1.c: Remove scan for tiled.

gcc/testsuite/gcc.target/aarch64/sve/pr94605.c

+/* { dg-options "-O2 -msve-vector-bits=256" } */
+
+typedef int v8si __attribute__((vector_size(32)));
+int g (v8si, v8si);
+
+void
+f (void)
+{
+  v8si x = {}, y = {};
+  while (g (x, y))
+    asm ("" : "+w" (x), "+w" (y));
+}