PR target/116275: Handle STV of *extenddi2_doubleword_highpart on i386.

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.

2024-08-12  Roger Sayle  <roger@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 *extendsi2_doubleword_highpart.

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

2 files changed, 33 insertions, 0 deletions

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});
+}