[x86 PATCH] PR target/116275: Handle STV of *extenddi2_doubleword_highpart

[Roger Sayle]

This patch resolves PR target/116275, a recent ICE-on-valid regression on
-m32 caused by my recent change to enable STV of DImode arithmeric right
shift on non-AVX512VL targets.  The oversight is that the i386 backend
contains an *extenddi2_doubleword_highpart instruction (whose pattern
is an arithmetic right shift of a left shift) that optimizes the case where
sign-extension need only update the highpart word of a DImode value when
generating 32-bit code (!TARGET_64BIT).  STV accepts this pattern as a
candidate, as there are patterns to handle this form of extension on SSE
using AVX512VL instructions (and previously ASHIFTRT was only allowed on
AVX512VL).  Now that ASHIFTRT is a candidate on non-AVX512vL targets, we
either need to check that the first operand is a register, or as done
below provide the define_insn_and_split that provides a non-AVX512VL
implementation of *extendv2di_highpart_stv.

The new testcase only ICEed with -m32, so this test could be limited to
target ia32, but there's no harm also running this test on -m64 to
provide a little extra test coverage.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2024-08-11  Roger Sayle  <ro...@nextmovesoftware.com>

gcc/ChangeLog
        PR target/116275
        * config/i386/i386.md (*extendv2di2_highpart_stv_noavx512vl): New
        define_insn_and_split to handle the STV conversion of the DImode
        pattern *extenddi2_doubleword_highpart.

gcc/testsuite/ChangeLog
        PR target/116275
        * g++.target/i386/pr116275.C: New test case.


Roger
--


diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index db7789c..1a6188f 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -17393,6 +17393,24 @@
        (ashift:V2DI (match_dup 1) (match_dup 2)))
    (set (match_dup 0)
        (ashiftrt:V2DI (match_dup 0) (match_dup 2)))])
+
+;; Without AVX512VL, split this instruction before reload.
+(define_insn_and_split "*extendv2di2_highpart_stv_noavx512vl"
+  [(set (match_operand:V2DI 0 "register_operand" "=v")
+       (ashiftrt:V2DI
+         (ashift:V2DI (match_operand:V2DI 1 "nonimmediate_operand" "vm")
+                      (match_operand:QI 2 "const_int_operand"))
+         (match_operand:QI 3 "const_int_operand")))]
+  "!TARGET_AVX512VL
+   && INTVAL (operands[2]) == INTVAL (operands[3])
+   && UINTVAL (operands[2]) < 32
+   && ix86_pre_reload_split ()"
+  "#"
+  "&& 1"
+  [(set (match_dup 0)
+       (ashift:V2DI (match_dup 1) (match_dup 2)))
+   (set (match_dup 0)
+       (ashiftrt:V2DI (match_dup 0) (match_dup 2)))])
 
 ;; Rotate instructions
 
diff --git a/gcc/testsuite/g++.target/i386/pr116275.C 
b/gcc/testsuite/g++.target/i386/pr116275.C
new file mode 100644
index 0000000..69c5b5a
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr116275.C
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mavx -std=c++11" } */
+
+struct SymbolDesc push_back(SymbolDesc);
+struct SymbolDesc {
+  long long ELFLocalSymIdx;
+};
+struct Expected {
+  long long &operator*();
+};
+void SymbolizableObjectFileaddSymbol() {
+  Expected SymbolAddressOrErr;
+  long long SymbolAddress = *SymbolAddressOrErr << 8 >> 8;
+  push_back({SymbolAddress});
+}