[X86] Pre-commit test case for bug in combineShiftRightArithmetic

It has been noticed that combineShiftRightArithmetic isn't dealing
properly with large shift amounts, as demonstrated by the test
case added in this commit.

I think the problem partly is related to X86 using i8 as shift amount
type during ISel. So shift amount larger then 127 may be treated
as negative shift amounts if not being careful.

Author: bjope

llvm/test/CodeGen/X86/sar_fold.ll

@@ -44,3 +44,47 @@ define i32 @shl24sar25(i32 %a) #0 {
   %2 = ashr exact i32 %1, 25
   ret i32 %2
 }
+
+define void @shl144sar48(ptr %p) #0 {
+; CHECK-LABEL: shl144sar48:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movswl (%eax), %ecx
+; CHECK-NEXT:    movl %ecx, %edx
+; CHECK-NEXT:    sarl $31, %edx
+; CHECK-NEXT:    shldl $2, %ecx, %edx
+; CHECK-NEXT:    shll $2, %ecx
+; CHECK-NEXT:    movl %ecx, 12(%eax)
+; CHECK-NEXT:    movl %edx, 16(%eax)
+; CHECK-NEXT:    movl $0, 8(%eax)
+; CHECK-NEXT:    movl $0, 4(%eax)
+; CHECK-NEXT:    movl $0, (%eax)
+; CHECK-NEXT:    retl
+  %a = load i160, ptr %p
+  %1 = shl i160 %a, 144
+  %2 = ashr exact i160 %1, 46
+  store i160 %2, ptr %p
+  ret void
+}
+
+; This is incorrect. The 142 least significant bits in the stored value should
+; be zero, and but 142-157 should be taken from %a with a sign-extend into the
+; two most significant bits.
+define void @shl144sar2(ptr %p) #0 {
+; CHECK-LABEL: shl144sar2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movswl (%eax), %ecx
+; CHECK-NEXT:    sarl $31, %ecx
+; CHECK-NEXT:    movl %ecx, 16(%eax)
+; CHECK-NEXT:    movl %ecx, 8(%eax)
+; CHECK-NEXT:    movl %ecx, 12(%eax)
+; CHECK-NEXT:    movl %ecx, 4(%eax)
+; CHECK-NEXT:    movl %ecx, (%eax)
+; CHECK-NEXT:    retl
+  %a = load i160, ptr %p
+  %1 = shl i160 %a, 144
+  %2 = ashr exact i160 %1, 2
+  store i160 %2, ptr %p
+  ret void
+}