Subzero: Improve handling of alloca instructions of constant size.

tests_lit/llvm2ice_tests/align-spill-locations.ll

 ; This checks to ensure that Subzero aligns spill slots.
 
 ; RUN: %p2i --filetype=obj --disassemble -i %s --args -Om1 | FileCheck %s
 ; RUN: %p2i --filetype=obj --disassemble -i %s --args -O2 | FileCheck %s
 
 ; The location of the stack slot for a variable is inferred from the
 ; return sequence.
 
 ; In this file, "global" refers to a variable with a live range across
 ; multiple basic blocks (not an LLVM global variable) and "local"
@@ skipping 22 matching lines @@
 ; CHECK-LABEL: align_local_vector
 ; CHECK: movups xmm0,XMMWORD PTR [esp]
 ; CHECK-NEXT: add esp,0x1c
 ; CHECK-NEXT: ret
 }
 
 declare void @ForceXmmSpills()
 
 define <4 x i32> @align_global_vector_ebp_based(i32 %arg) {
 entry:
+  br label %eblock  ; Disable alloca optimization
+eblock:
   %alloc = alloca i8, i32 1, align 1
   %vec.global = insertelement <4 x i32> undef, i32 %arg, i32 0
   br label %block
 block:
   call void @ForceXmmSpillsAndUseAlloca(i8* %alloc)
   ret <4 x i32> %vec.global
 ; CHECK-LABEL: align_global_vector_ebp_based
 ; CHECK: movups xmm0,XMMWORD PTR [ebp-0x18]
 ; CHECK-NEXT: mov esp,ebp
 ; CHECK-NEXT: pop ebp
 ; CHECK: ret
 }
 
 define <4 x i32> @align_local_vector_ebp_based(i32 %arg) {
 entry:
+  br label %eblock  ; Disable alloca optimization
+eblock:
   %alloc = alloca i8, i32 1, align 1
   %vec.local = insertelement <4 x i32> undef, i32 %arg, i32 0
   call void @ForceXmmSpillsAndUseAlloca(i8* %alloc)
   ret <4 x i32> %vec.local
 ; CHECK-LABEL: align_local_vector_ebp_based
 ; CHECK: movups xmm0,XMMWORD PTR [ebp-0x18]
 ; CHECK-NEXT: mov esp,ebp
 ; CHECK-NEXT: pop ebp
 ; CHECK: ret
 }
@@ skipping 10 matching lines @@
 ; CHECK-LABEL: align_local_vector_and_global_float
 ; CHECK: cvtsi2ss xmm0,eax
 ; CHECK-NEXT: movss DWORD PTR [esp+{{0xc|0x1c}}],xmm0
 ; CHECK: movups xmm0,XMMWORD PTR [{{esp|esp\+0x10}}]
 ; CHECK-NEXT: add esp,0x2c
 ; CHECK-NEXT: ret
 }
 
 declare void @ForceXmmSpillsAndUseAlloca(i8*)
 declare void @ForceXmmSpillsAndUseFloat(float)