From 97874bddd63328616c18a0e8230f6732c02ba3ba Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed.bougacha@gmail.com>
Date: Mon, 27 Mar 2017 17:31:56 +0000
Subject: [PATCH] [GlobalISel][AArch64] Fold FI into LDR/STR ui addressing
 mode.

A majority of loads and stores at O0 access an alloca.

It's trivial to fold the G_FRAME_INDEX into the instruction; do it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298864 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../AArch64/AArch64InstructionSelector.cpp    |  5 +++
 .../AArch64/GlobalISel/select-load.mir        | 33 +++++++++++++++++++
 .../AArch64/GlobalISel/select-store.mir       | 33 +++++++++++++++++++
 3 files changed, 71 insertions(+)

diff --git a/lib/Target/AArch64/AArch64InstructionSelector.cpp b/lib/Target/AArch64/AArch64InstructionSelector.cpp
index be0f6eb44d1..70c11c125ef 100644
--- a/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -792,6 +792,11 @@ bool AArch64InstructionSelector::select(MachineInstr &I) const {
       }
     }
 
+    // If we haven't folded anything into our addressing mode yet, try to fold
+    // a frame index into the base+offset.
+    if (!Offset && PtrMI->getOpcode() == TargetOpcode::G_FRAME_INDEX)
+      I.getOperand(1).ChangeToFrameIndex(PtrMI->getOperand(1).getIndex());
+
     I.addOperand(MachineOperand::CreateImm(Offset));
 
     // If we're storing a 0, use WZR/XZR.
diff --git a/test/CodeGen/AArch64/GlobalISel/select-load.mir b/test/CodeGen/AArch64/GlobalISel/select-load.mir
index 09b40201f9a..9188e2b0c0f 100644
--- a/test/CodeGen/AArch64/GlobalISel/select-load.mir
+++ b/test/CodeGen/AArch64/GlobalISel/select-load.mir
@@ -8,6 +8,11 @@
   define void @load_s16_gpr(i16* %addr) { ret void }
   define void @load_s8_gpr(i8* %addr) { ret void }
 
+  define void @load_fi_s64_gpr() {
+    %ptr0 = alloca i64
+    ret void
+  }
+
   define void @load_gep_128_s64_gpr(i64* %addr) { ret void }
   define void @load_gep_512_s32_gpr(i32* %addr) { ret void }
   define void @load_gep_64_s16_gpr(i16* %addr) { ret void }
@@ -125,6 +130,34 @@ body:             |
     %w0 = COPY %1(s8)
 ...
 
+---
+# CHECK-LABEL: name: load_fi_s64_gpr
+name:            load_fi_s64_gpr
+legalized:       true
+regBankSelected: true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr }
+# CHECK-NEXT:  - { id: 1, class: gpr64 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+stack:
+  - { id: 0, name: ptr0, offset: 0, size: 8, alignment: 8 }
+
+# CHECK:  body:
+# CHECK: %1 = LDRXui %stack.0.ptr0, 0 :: (load 8)
+# CHECK: %x0 = COPY %1
+body:             |
+  bb.0:
+    liveins: %x0
+
+    %0(p0) = G_FRAME_INDEX %stack.0.ptr0
+    %1(s64) = G_LOAD %0 :: (load 8)
+    %x0 = COPY %1(s64)
+...
+
 ---
 # CHECK-LABEL: name: load_gep_128_s64_gpr
 name:            load_gep_128_s64_gpr
diff --git a/test/CodeGen/AArch64/GlobalISel/select-store.mir b/test/CodeGen/AArch64/GlobalISel/select-store.mir
index d40a1231df2..9b8f5c566ce 100644
--- a/test/CodeGen/AArch64/GlobalISel/select-store.mir
+++ b/test/CodeGen/AArch64/GlobalISel/select-store.mir
@@ -11,6 +11,11 @@
   define void @store_zero_s64_gpr(i64* %addr) { ret void }
   define void @store_zero_s32_gpr(i32* %addr) { ret void }
 
+  define void @store_fi_s64_gpr() {
+    %ptr0 = alloca i64
+    ret void
+  }
+
   define void @store_gep_128_s64_gpr(i64* %addr) { ret void }
   define void @store_gep_512_s32_gpr(i32* %addr) { ret void }
   define void @store_gep_64_s16_gpr(i16* %addr) { ret void }
@@ -183,6 +188,34 @@ body:             |
 
 ...
 
+---
+# CHECK-LABEL: name: store_fi_s64_gpr
+name:            store_fi_s64_gpr
+legalized:       true
+regBankSelected: true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr64 }
+# CHECK-NEXT:  - { id: 1, class: gpr }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+stack:
+  - { id: 0, name: ptr0, offset: 0, size: 8, alignment: 8 }
+
+# CHECK:  body:
+# CHECK: %0 = COPY %x0
+# CHECK: STRXui %0, %stack.0.ptr0, 0 :: (store 8)
+body:             |
+  bb.0:
+    liveins: %x0
+
+    %0(p0) = COPY %x0
+    %1(p0) = G_FRAME_INDEX %stack.0.ptr0
+    G_STORE  %0, %1 :: (store 8)
+...
+
 ---
 # CHECK-LABEL: name: store_gep_128_s64_gpr
 name:            store_gep_128_s64_gpr
-- 
2.50.1