[PATCH, AArch64] Improve handling of constants destined for FP_REGS

[Ian Bolton]

(This patch supercedes this one:
http://gcc.gnu.org/ml/gcc-patches/2013-07/msg01462.html)

The movdi_aarch64 pattern allows moving a constant into an FP_REG,
but has the constraint Dd, which is stricter than the constraint N for
moving a constant into a CORE_REG.  This is due to restricted values
allowed for MOVI instruction.

Due to the predicate allowing any constant that is valid for the
CORE_REGs, we can run into situations where IRA/reload has decided
to use FP_REGs but the value is not actually valid for MOVI.

This patch makes use of TARGET_PREFERRED_RELOAD_CLASS to ensure that
NO_REGS (which leads to literal pool) is returned, when the immediate
can't be put directly into FP_REGS.

A testcase is included.

Linux regressions all came back good.

OK for trunk?

Cheers,
Ian


2013-09-04  Ian Bolton  <ian.bol...@arm.com>

gcc/
        * config/aarch64/aarch64.c (aarch64_preferred_reload_class):
        Return NO_REGS for immediate that can't be moved directly
        into FP_REGS.

testsuite/
        * gcc.target/aarch64/movdi_1.c: New test.
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index aed035a..2c07ccf 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -4236,10 +4236,18 @@ aarch64_class_max_nregs (reg_class_t regclass, enum 
machine_mode mode)
 }
 
 static reg_class_t
-aarch64_preferred_reload_class (rtx x ATTRIBUTE_UNUSED, reg_class_t regclass)
+aarch64_preferred_reload_class (rtx x, reg_class_t regclass)
 {
-  return ((regclass == POINTER_REGS || regclass == STACK_REG)
-         ? GENERAL_REGS : regclass);
+  if (regclass == POINTER_REGS || regclass == STACK_REG)
+    return GENERAL_REGS;
+
+  /* If it's an integer immediate that MOVI can't handle, then
+     FP_REGS is not an option, so we return NO_REGS instead.  */
+  if (CONST_INT_P (x) && reg_class_subset_p (regclass, FP_REGS)
+      && !aarch64_simd_imm_scalar_p (x, GET_MODE (x)))
+    return NO_REGS;
+
+  return regclass;
 }
 
 void
diff --git a/gcc/testsuite/gcc.target/aarch64/movdi_1.c 
b/gcc/testsuite/gcc.target/aarch64/movdi_1.c
new file mode 100644
index 0000000..a22378d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/movdi_1.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-inline" } */
+
+#include <arm_neon.h>
+
+void
+foo1 (uint64_t *a)
+{
+  uint64x1_t val18;
+  uint32x2_t val19;
+  uint64x1_t val20;
+  val19 = vcreate_u32 (0x800000004cf3dffbUL);
+  val20 = vrsra_n_u64 (val18, vreinterpret_u64_u32 (val19), 34);
+  vst1_u64 (a, val20);
+}
+
+void
+foo2 (uint64_t *a)
+{
+  uint64x1_t val18;
+  uint32x2_t val19;
+  uint64x1_t val20;
+  val19 = vcreate_u32 (0xdffbUL);
+  val20 = vrsra_n_u64 (val18, vreinterpret_u64_u32 (val19), 34);
+  vst1_u64 (a, val20);
+}