From: Richard Biener <rguenther@suse.de>
Date: Wed, 28 Aug 2024 12:06:48 +0000 (+0200)
Subject: tree-optimization/116514 - handle pointer difference in bit-CCP
X-Git-Tag: basepoints/gcc-16~6005
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e7d5b9aa021f6fc32810670b18ffabe543262775;p=thirdparty%2Fgcc.git

tree-optimization/116514 - handle pointer difference in bit-CCP

When evaluating the difference of two aligned pointers in CCP we
fail to handle the EXACT_DIV_EXPR by the element size that occurs.
The testcase then also exercises modulo to test alignment but
modulo by a power-of-two isn't handled either.

	PR tree-optimization/116514
	* tree-ssa-ccp.cc (bit_value_binop): Handle EXACT_DIV_EXPR
	like TRUNC_DIV_EXPR.  Handle exact division of a signed value
	by a power-of-two like a shift.  Handle unsigned division by
	a power-of-two like a shift.
	Handle unsigned TRUNC_MOD_EXPR by power-of-two, handle signed
	TRUNC_MOD_EXPR by power-of-two if the result is zero.

	* gcc.dg/tree-ssa/ssa-ccp-44.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
new file mode 100644
index 00000000000..f1f09bfb117
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-ccp1" } */
+
+int
+test(int* a, int* b)
+{
+  __INTPTR_TYPE__ delta = (int*)__builtin_assume_aligned(b, 32)
+               - (int*)__builtin_assume_aligned(a, 32);
+  __INTPTR_TYPE__ x = delta % 8;
+  return (x == 0);
+}
+
+/* { dg-final { scan-tree-dump "return 1;" "ccp1" } } */
diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
index 47b2ce9441e..a5f6ef5f5dd 100644
--- a/gcc/tree-ssa-ccp.cc
+++ b/gcc/tree-ssa-ccp.cc
@@ -1921,6 +1921,27 @@ bit_value_binop (enum tree_code code, signop sgn, int width,
       {
 	widest_int r1max = r1val | r1mask;
 	widest_int r2max = r2val | r2mask;
+	if (r2mask == 0)
+	  {
+	    widest_int shift = wi::exact_log2 (r2val);
+	    if (shift != -1)
+	      {
+		// Handle modulo by a power of 2 as a bitwise and.
+		widest_int tem_val, tem_mask;
+		bit_value_binop (BIT_AND_EXPR, sgn, width, &tem_val, &tem_mask,
+				 r1type_sgn, r1type_precision, r1val, r1mask,
+				 r2type_sgn, r2type_precision,
+				 r2val - 1, r2mask);
+		if (sgn == UNSIGNED
+		    || !wi::neg_p (r1max)
+		    || (tem_mask == 0 && tem_val == 0))
+		  {
+		    *val = tem_val;
+		    *mask = tem_mask;
+		    return;
+		  }
+	      }
+	  }
 	if (sgn == UNSIGNED
 	    || (!wi::neg_p (r1max) && !wi::neg_p (r2max)))
 	  {
@@ -1949,11 +1970,15 @@ bit_value_binop (enum tree_code code, signop sgn, int width,
 	}
       break;
 
+    case EXACT_DIV_EXPR:
     case TRUNC_DIV_EXPR:
       {
 	widest_int r1max = r1val | r1mask;
 	widest_int r2max = r2val | r2mask;
-	if (r2mask == 0 && !wi::neg_p (r1max))
+	if (r2mask == 0
+	    && (code == EXACT_DIV_EXPR
+		|| sgn == UNSIGNED
+		|| !wi::neg_p (r1max)))
 	  {
 	    widest_int shift = wi::exact_log2 (r2val);
 	    if (shift != -1)