rtlanal: Don't assume that calls write to a global SP [PR99596]

This patch is a GCC 11 regression caused by the rtl-ssa code.
Normally we treat calls as containing a potential set of a global
register, but DF makes a sensible exception for the stack pointer:

      if (i == STACK_POINTER_REGNUM)
	/* The stack ptr is used (honorarily) by a CALL insn.  */
	df_ref_record (DF_REF_BASE, collection_rec, regno_reg_rtx[i],
		       NULL, bb, insn_info, DF_REF_REG_USE,
		       DF_REF_CALL_STACK_USAGE | flags);
      else if (global_regs[i])
	{
	  /* Calls to const functions cannot access any global registers and
	     calls to pure functions cannot set them.  All other calls may
	     reference any of the global registers, so they are recorded as
	     used. */

The only DF definition of SP was therefore the one in the entry block.
However, the rtlanal.c rtx_properties code (wrongly) assumed that calls
also clobbered the global SP.  This led to multiple definitions of SP
when we only expected one.

This patch tightens the rtlanal.c handling of global registers
to match the DF approach.

gcc/
	PR rtl-optimization/99596
	* rtlanal.c (rtx_properties::try_to_add_insn): Don't add global
	register accesses for const calls.  Assume that pure functions
	can only read from global registers.  Ignore cases in which
	the stack pointer has been marked global.

gcc/testsuite/
	PR rtl-optimization/99596
	* gcc.target/arm/pr99596.c: New test.

diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index c35386bccbdb921b04db8f6a6f82ec37d4c3c675..170420a610b953e99a427e5034d3716053316c21 100644 (file)
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -2311,15 +2311,25 @@ rtx_properties::try_to_add_insn (const rtx_insn *insn, bool include_notes)
 {
   if (CALL_P (insn))
     {
-      /* Adding the global registers first removes a situation in which
+      /* Non-const functions can read from global registers.  Impure
+        functions can also set them.
+
+        Adding the global registers first removes a situation in which
         a fixed-form clobber of register R could come before a real set
         of register R.  */
-      if (!hard_reg_set_empty_p (global_reg_set))
+      if (!hard_reg_set_empty_p (global_reg_set)
+         && !RTL_CONST_CALL_P (insn))
        {
-         unsigned int flags = (rtx_obj_flags::IS_READ
-                               | rtx_obj_flags::IS_WRITE);
+         unsigned int flags = rtx_obj_flags::IS_READ;
+         if (!RTL_PURE_CALL_P (insn))
+           flags |= rtx_obj_flags::IS_WRITE;
          for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
-           if (global_regs[regno] && ref_iter != ref_end)
+           /* As a special case, the stack pointer is invariant across calls
+              even if it has been marked global; see the corresponding
+              handling in df_get_call_refs.  */
+           if (regno != STACK_POINTER_REGNUM
+               && global_regs[regno]
+               && ref_iter != ref_end)
              *ref_iter++ = rtx_obj_reference (regno, flags,
                                               reg_raw_mode[regno], 0);
        }

diff --git a/gcc/testsuite/gcc.target/arm/pr99596.c b/gcc/testsuite/gcc.target/arm/pr99596.c
new file mode 100644 (file)
index 0000000..2b8b4c8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/pr99596.c
@@ -0,0 +1,18 @@
+/* { dg-options "-Os -mtune=xscale" } */
+
+register int a asm("sp");
+extern int b;
+typedef struct {
+  long c[16 * 8 / 32];
+} d;
+int e;
+int f;
+int g;
+d h;
+int j(int, int, int, d);
+int i(void) {
+  for (;;) {
+    b &&j(e, f, g, h);
+    j(e, f, g, h);
+  }
+}