Re: [PATCH] regcprop: Fix another cprop_hardreg bug [PR100342]

[Jakub Jelinek <jakub@redhat.com>]

On Wed, May 05, 2021 at 07:44:46PM +0200, Jakub Jelinek via Gcc-patches wrote:
> So perhaps just the vd->e[dr].mode in there could change to
> GET_MODE (src) and drop the previous PR98694 change?

I've bootstrapped/regtested that successfully on the trunk
(on {x86_64,i686}-linux), though haven't attempted to merge the two comments:

2021-05-06  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/100342
	* regcprop.c (copy_value): When copying a source reg in a wider
	mode than it has recorded for the value, adjust recorded destination
	mode too.

	* gcc.target/i386/pr100342.c: New test.

--- gcc/regcprop.c.jj	2020-04-30 17:41:37.624675304 +0200
+++ gcc/regcprop.c	2021-05-05 16:24:01.667308941 +0200
@@ -382,10 +382,22 @@ copy_value (rtx dest, rtx src, struct va
      (set (reg:HI R5) (reg:HI R[0-4]))
 
      in which all registers have only 16 defined bits.  */
-  else if (partial_subreg_p (vd->e[sr].mode, GET_MODE (src))
-	   && partial_subreg_p (vd->e[sr].mode,
-				vd->e[vd->e[sr].oldest_regno].mode))
-    return;
+
+  /* If a narrower value is copied using wider mode, the upper bits
+     are undefined (could be e.g. a former paradoxical subreg).  Signal
+     in that case we've only copied value using the narrower mode.
+     Consider:
+     (set (reg:DI r14) (mem:DI ...))
+     (set (reg:QI si) (reg:QI r14))
+     (set (reg:DI bp) (reg:DI r14))
+     (set (reg:DI r14) (const_int ...))
+     (set (reg:DI dx) (reg:DI si))
+     (set (reg:DI si) (const_int ...))
+     (set (reg:DI dx) (reg:DI bp))
+     The last set is not redundant, while the low 8 bits of dx are already
+     equal to low 8 bits of bp, the other bits are undefined.  */
+  else if (partial_subreg_p (vd->e[sr].mode, GET_MODE (src)))
+    set_value_regno (dr, vd->e[sr].mode, vd);
 
   /* Link DR at the end of the value chain used by SR.  */
 
--- gcc/testsuite/gcc.target/i386/pr100342.c.jj	2021-05-05 17:01:29.139356719 +0200
+++ gcc/testsuite/gcc.target/i386/pr100342.c	2021-05-05 17:01:14.287521150 +0200
@@ -0,0 +1,70 @@
+/* PR rtl-optimization/100342 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O2 -fno-dse -fno-forward-propagate -Wno-psabi -mno-sse2" } */
+
+#define SHL(x, y) ((x) << ((y) & (sizeof(x) * 8 - 1)))
+#define SHR(x, y) ((x) >> ((y) & (sizeof(x) * 8 - 1)))
+#define ROR(x, y) (SHR(x, y)) | (SHL(x, (sizeof(x) * 8 - (y))))
+#define SHLV(x, y) ((x) << ((y) & (sizeof((x)[0]) * 8 - 1)))
+#define SHLSV(x, y) ((x) << ((y) & (sizeof((y)[0]) * 8 - 1)))
+typedef unsigned char A;
+typedef unsigned char __attribute__((__vector_size__ (8))) B;
+typedef unsigned char __attribute__((__vector_size__ (16))) C;
+typedef unsigned char __attribute__((__vector_size__ (32))) D;
+typedef unsigned char __attribute__((__vector_size__ (64))) E;
+typedef unsigned short F;
+typedef unsigned short __attribute__((__vector_size__ (16))) G;
+typedef unsigned int H;
+typedef unsigned int __attribute__((__vector_size__ (32))) I;
+typedef unsigned long long J;
+typedef unsigned long long __attribute__((__vector_size__ (8))) K;
+typedef unsigned long long __attribute__((__vector_size__ (32))) L;
+typedef unsigned long long __attribute__((__vector_size__ (64))) M;
+typedef unsigned __int128 N;
+typedef unsigned __int128 __attribute__((__vector_size__ (16))) O;
+typedef unsigned __int128 __attribute__((__vector_size__ (32))) P;
+typedef unsigned __int128 __attribute__((__vector_size__ (64))) Q;
+B v1;
+D v2;
+L v3;
+K v4;
+I v5;
+O v6;
+
+B
+foo (A a, C b, E c, F d, G e, H f, J g, M h, N i, P j, Q k)
+{
+  b &= (A) f;
+  k += a;
+  G l = e;
+  D m = v2 >= (A) (J) v1;
+  J r = a + g;
+  L n = v3 <= f;
+  k -= i / f;
+  l -= (A) g;
+  c |= (A) d;
+  b -= (A) i;
+  J o = ROR (__builtin_clz (r), a);
+  K p = v4 | f, q = v4 <= f;
+  P s = SHLV (SHLSV (__builtin_bswap64 (i), (P) (0 < j)) <= 0, j);
+  n += a <= r;
+  M t = (M) (a / SHLV (c, 0)) != __builtin_bswap64 (i);
+  I u = f - v5;
+  E v = (E) h + (E) t + (E) k;
+  D w = (union { D b[2]; }) { }.b[0] + ((union { E b; }) v).b[1] + m + (D) u + (D) n + (D) s;
+  C x = ((union { D b; }) w).b[1] + b + (C) l + (C) v6;
+  B y = ((union { C a; B b; }) x).b + ((union { C a; B b[2]; }) x).b[1] + (B) p + (B) q;
+  J z = i + o;
+  F z2 = z;
+  A z3 = z2;
+  return y + z3;
+}
+
+int
+main ()
+{
+  B x = foo (0, (C) { }, (E) { }, 10, (G) { }, 4, 2, (M) { }, 123842323652213865LL, (P) { 1 }, (Q) { });
+  if ((J) x != 0x2e2c2e2c2e2c2e30ULL)
+    __builtin_abort();
+  return 0;
+}


	Jakub