In code like the following from KVM:
/* it is a read fault? */
error_code = (exit_qualification << 2) & PFERR_FETCH_MASK;
it would be nicer to write
/* it is a read fault? */
error_code = (exit_qualification & VMX_EPT_READ_FAULT_MASK) ?
PFERR_FETCH_MASK : 0;
instead of having to know the difference between the positions of the
source and destination bits. LLVM catches the latter just fine (which
is why I am sending this in stage 3...), but GCC does not, so this
patch adds two patterns to catch it.
The combine.c hunk of v1 has been committed already.
Bootstrapped/regtested x86_64-pc-linux-gnu, ok?
Paolo
2016-11-26 Paolo Bonzini <bonz...@gnu.org>
* match.pd: Simplify X ? C : 0 where C is a power of 2 and
X tests a single bit.
2016-11-26 Paolo Bonzini <bonz...@gnu.org>
* gcc.dg/fold-and-lshift.c, gcc.dg/fold-and-rshift-1.c,
gcc.dg/fold-and-rshift-2.c: New testcases.
Index: match.pd
===================================================================
--- match.pd (revision 242916)
+++ match.pd (working copy)
@@ -2630,6 +2630,21 @@
(cmp (bit_and@2 @0 integer_pow2p@1) @1)
(icmp @2 { build_zero_cst (TREE_TYPE (@0)); })))
+/* If we have (A & C) != 0 ? D : 0 where C and D are powers of 2,
+ convert this into a shift followed by ANDing with D. */
+(simplify
+ (cond
+ (ne (bit_and @0 integer_pow2p@1) integer_zerop)
+ integer_pow2p@2 integer_zerop)
+ (with {
+ int shift = wi::exact_log2 (@2) - wi::exact_log2 (@1);
+ }
+ (if (shift > 0)
+ (bit_and
+ (lshift (convert @0) { build_int_cst (integer_type_node, shift); }) @2)
+ (bit_and
+ (convert (rshift @0 { build_int_cst (integer_type_node, -shift); })) @2))))
+
/* If we have (A & C) != 0 where C is the sign bit of A, convert
this into A < 0. Similarly for (A & C) == 0 into A >= 0. */
(for cmp (eq ne)
@@ -2644,6 +2659,19 @@
(with { tree stype = signed_type_for (TREE_TYPE (@0)); }
(ncmp (convert:stype @0) { build_zero_cst (stype); })))))
+/* If we have A < 0 ? C : 0 where C is a power of 2, convert
+ this into a right shift followed by ANDing with C. */
+(simplify
+ (cond
+ (lt @0 integer_zerop)
+ integer_pow2p@1 integer_zerop)
+ (with {
+ int shift = element_precision (@0) - wi::exact_log2 (@1) - 1;
+ }
+ (bit_and
+ (convert (rshift @0 { build_int_cst (integer_type_node, shift); }))
+ @1)))
+
/* When the addresses are not directly of decls compare base and offset.
This implements some remaining parts of fold_comparison address
comparisons but still no complete part of it. Still it is good
Index: testsuite/gcc.dg/fold-and-lshift.c
===================================================================
--- testsuite/gcc.dg/fold-and-lshift.c (revision 0)
+++ testsuite/gcc.dg/fold-and-lshift.c (working copy)
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+int f(int x)
+{
+ return (x << 2) & 128;
+}
+
+int g(int x)
+{
+ return !!(x & 32) << 7;
+}
+
+int h(int x)
+{
+ return ((x >> 5) & 1) << 7;
+}
+
+int i(int x)
+{
+ return (x & 32) >> 5 << 7;
+}
+
+int j(int x)
+{
+ return ((x >> 5) & 1) ? 128 : 0;
+}
+
+int k(int x)
+{
+ return (x & 32) ? 128 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
+/* { dg-final { scan-assembler-not "sarl" { target i?86-*-* x86_64-*-* } } }"
*/
Index: testsuite/gcc.dg/fold-and-rshift-1.c
===================================================================
--- testsuite/gcc.dg/fold-and-rshift-1.c (revision 0)
+++ testsuite/gcc.dg/fold-and-rshift-1.c (working copy)
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+int f(int x)
+{
+ return (x >> 2) & 128;
+}
+
+int g(int x)
+{
+ return !!(x & 512) << 7;
+}
+
+int h(int x)
+{
+ return ((x >> 9) & 1) << 7;
+}
+
+int i(int x)
+{
+ return (x & 512) >> 9 << 7;
+}
+
+int j(int x)
+{
+ return ((x >> 9) & 1) ? 128 : 0;
+}
+
+int k(int x)
+{
+ return (x & 512) ? 128 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
+/* { dg-final { scan-assembler-not "sall" { target i?86-*-* x86_64-*-* } } }"
*/
Index: testsuite/gcc.dg/fold-and-rshift-2.c
===================================================================
--- testsuite/gcc.dg/fold-and-rshift-2.c (revision 0)
+++ testsuite/gcc.dg/fold-and-rshift-2.c (working copy)
@@ -0,0 +1,25 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+unsigned f(unsigned x)
+{
+ return (x >> 29) & 32;
+}
+
+unsigned g(unsigned x)
+{
+ return !!(x & 0x80000000) << 5;
+}
+
+unsigned j(unsigned x)
+{
+ return ((x >> 31) & 1) ? 32 : 0;
+}
+
+unsigned k(unsigned x)
+{
+ return (x & 0x80000000) ? 32 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not " \\? " "original" } } */
+/* { dg-final { scan-assembler-not "sall" { target i?86-*-* x86_64-*-* } } }"
*/
