[ARM] Avoid spilling lr with Thumb1 tail calls.

Normally, if any registers are spilled, we prefer to spill lr on Thumb1
so we can fold the "bx lr" into the "pop".  However, if there are tail
calls involved, restoring lr is expensive, so skip the optimization in
that case.

The spill of r7 in the new test also isn't necessary, but that's
mostly orthogonal to this patch. (It's the same code in
ARMFrameLowering, but it's not related to tail calls.)

Differential Revision: https://reviews.llvm.org/D49459

llvm-svn: 339283

diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index a8c7570..40de21e 100644 (file)
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -1920,9 +1920,13 @@ void ARMFrameLowering::determineCalleeSaves(MachineFunction &MF,
                         << "\n");
     }
 
+    // Avoid spilling LR in Thumb1 if there's a tail call: it's expensive to
+    // restore LR in that case.
+    bool ExpensiveLRRestore = AFI->isThumb1OnlyFunction() && MFI.hasTailCall();
+
     // If LR is not spilled, but at least one of R4, R5, R6, and R7 is spilled.
     // Spill LR as well so we can fold BX_RET to the registers restore (LDM).
-    if (!LRSpilled && CS1Spilled) {
+    if (!LRSpilled && CS1Spilled && !ExpensiveLRRestore) {
       SavedRegs.set(ARM::LR);
       NumGPRSpills++;
       SmallVectorImpl<unsigned>::iterator LRPos;
@@ -1948,7 +1952,8 @@ void ARMFrameLowering::determineCalleeSaves(MachineFunction &MF,
           // Windows on ARM, accept R11 (frame pointer)
           if (!AFI->isThumbFunction() ||
               (STI.isTargetWindows() && Reg == ARM::R11) ||
-              isARMLowRegister(Reg) || Reg == ARM::LR) {
+              isARMLowRegister(Reg) ||
+              (Reg == ARM::LR && !ExpensiveLRRestore)) {
             SavedRegs.set(Reg);
             LLVM_DEBUG(dbgs() << "Spilling " << printReg(Reg, TRI)
                               << " to make up alignment\n");

diff --git a/llvm/test/CodeGen/ARM/v8m-tail-call.ll b/llvm/test/CodeGen/ARM/v8m-tail-call.ll
index f4d3a45..7ee80d4 100644 (file)
--- a/llvm/test/CodeGen/ARM/v8m-tail-call.ll
+++ b/llvm/test/CodeGen/ARM/v8m-tail-call.ll
@@ -1,34 +1,65 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc %s -o - -mtriple=thumbv8m.base | FileCheck %s
 
 declare i32 @g(...)
 
 declare i32 @h0(i32, i32, i32, i32)
 define hidden i32 @f0() {
+; CHECK-LABEL: f0:
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    bl g
+; CHECK-NEXT:    movs r1, #1
+; CHECK-NEXT:    movs r2, #2
+; CHECK-NEXT:    movs r3, #3
+; CHECK-NEXT:    ldr r7, [sp, #4]
+; CHECK-NEXT:    mov lr, r7
+; CHECK-NEXT:    pop {r7}
+; CHECK-NEXT:    add sp, #4
+; CHECK-NEXT:    b h0
   %1 = tail call i32 bitcast (i32 (...)* @g to i32 ()*)()
   %2 = tail call i32 @h0(i32 %1, i32 1, i32 2, i32 3)
   ret i32 %2
-; CHECK-LABEL: f0
-; CHECK:      ldr     [[POP:r[4567]]], [sp, #4]
-; CHECK-NEXT: mov     lr, [[POP]]
-; CHECK-NEXT: pop     {{.*}}[[POP]]
-; CHECK-NEXT: add     sp, #4
-; CHECK-NEXT: b       h0
 }
 
 declare i32 @h1(i32)
 define hidden i32 @f1() {
+; CHECK-LABEL: f1:
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    bl g
+; CHECK-NEXT:    pop {r7}
+; CHECK-NEXT:    pop {r1}
+; CHECK-NEXT:    mov lr, r1
+; CHECK-NEXT:    b h1
   %1 = tail call i32 bitcast (i32 (...)* @g to i32 ()*)()
   %2 = tail call i32 @h1(i32 %1)
   ret i32 %2
-; CHECK-LABEL: f1
-; CHECK: pop     {r7}
-; CHECK: pop     {r1}
-; CHECK: mov     lr, r1
-; CHECK: b       h1
 }
 
 declare i32 @h2(i32, i32, i32, i32, i32)
 define hidden i32 @f2(i32, i32, i32, i32, i32) {
+; CHECK-LABEL: f2:
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r4, r5, r6, lr}
+; CHECK-NEXT:    mov r4, r3
+; CHECK-NEXT:    mov r5, r2
+; CHECK-NEXT:    mov r6, r1
+; CHECK-NEXT:    bl g
+; CHECK-NEXT:    cbz r0, .LBB2_2
+; CHECK-NEXT:  @ %bb.1:
+; CHECK-NEXT:    mov r1, r6
+; CHECK-NEXT:    mov r2, r5
+; CHECK-NEXT:    mov r3, r4
+; CHECK-NEXT:    ldr r4, [sp, #12]
+; CHECK-NEXT:    mov lr, r4
+; CHECK-NEXT:    pop {r4, r5, r6}
+; CHECK-NEXT:    add sp, #4
+; CHECK-NEXT:    b h2
+; CHECK-NEXT:  .LBB2_2:
+; CHECK-NEXT:    movs r0, #0
+; CHECK-NEXT:    mvns r0, r0
+; CHECK-NEXT:    pop {r4, r5, r6, pc}
   %6 = tail call i32 bitcast (i32 (...)* @g to i32 ()*)()
   %7 = icmp eq i32 %6, 0
   br i1 %7, label %10, label %8
@@ -38,12 +69,6 @@ define hidden i32 @f2(i32, i32, i32, i32, i32) {
 
   %11 = phi i32 [ %9, %8 ], [ -1, %5 ]
   ret i32 %11
-; CHECK-LABEL: f2
-; CHECK:      ldr     [[POP:r[4567]]], [sp, #12]
-; CHECK-NEXT: mov     lr, [[POP]]
-; CHECK-NEXT: pop     {{.*}}[[POP]]
-; CHECK-NEXT: add     sp, #4
-; CHECK-NEXT: b       h2
 }
 
 ; Make sure that tail calls to function pointers that require r0-r3 for argument
@@ -51,7 +76,17 @@ define hidden i32 @f2(i32, i32, i32, i32, i32) {
 @fnptr = global i32 (i32, i32, i32, i32)* null
 define i32 @test3() {
 ; CHECK-LABEL: test3:
-; CHECK: blx {{r[0-9]+}}
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r4, lr}
+; CHECK-NEXT:    movw r0, :lower16:fnptr
+; CHECK-NEXT:    movt r0, :upper16:fnptr
+; CHECK-NEXT:    ldr r4, [r0]
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r1, #2
+; CHECK-NEXT:    movs r2, #3
+; CHECK-NEXT:    movs r3, #4
+; CHECK-NEXT:    blx r4
+; CHECK-NEXT:    pop {r4, pc}
   %1 = load i32 (i32, i32, i32, i32)*, i32 (i32, i32, i32, i32)** @fnptr
   %2 = tail call i32 %1(i32 1, i32 2, i32 3, i32 4)
   ret i32 %2
@@ -60,7 +95,17 @@ define i32 @test3() {
 @fnptr2 = global i32 (i32, i32, i64)* null
 define i32 @test4() {
 ; CHECK-LABEL: test4:
-; CHECK: blx {{r[0-9]+}}
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r4, lr}
+; CHECK-NEXT:    movw r0, :lower16:fnptr2
+; CHECK-NEXT:    movt r0, :upper16:fnptr2
+; CHECK-NEXT:    ldr r4, [r0]
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r1, #2
+; CHECK-NEXT:    movs r2, #3
+; CHECK-NEXT:    movs r3, #0
+; CHECK-NEXT:    blx r4
+; CHECK-NEXT:    pop {r4, pc}
   %1 = load i32 (i32, i32, i64)*, i32 (i32, i32, i64)** @fnptr2
   %2 = tail call i32 %1(i32 1, i32 2, i64 3)
   ret i32 %2
@@ -72,9 +117,13 @@ define i32 @test4() {
 @fnptr3 = global i32 (i32, i32)* null
 define i32 @test5() {
 ; CHECK-LABEL: test5:
-; CHECK: ldr [[REG:r[0-9]+]]
-; CHECK: bx [[REG]]
-; CHECK-NOT: blx [[REG]]
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    movw r0, :lower16:fnptr3
+; CHECK-NEXT:    movt r0, :upper16:fnptr3
+; CHECK-NEXT:    ldr r2, [r0]
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r1, #2
+; CHECK-NEXT:    bx r2
   %1 = load i32 (i32, i32)*, i32 (i32, i32)** @fnptr3
   %2 = tail call i32 %1(i32 1, i32 2)
   ret i32 %2
@@ -84,9 +133,14 @@ define i32 @test5() {
 @fnptr4 = global i32 (i32, i64)* null
 define i32 @test6() {
 ; CHECK-LABEL: test6:
-; CHECK: ldr [[REG:r[0-9]+]]
-; CHECK: bx [[REG]]
-; CHECK-NOT: blx [[REG]]
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    movw r0, :lower16:fnptr4
+; CHECK-NEXT:    movt r0, :upper16:fnptr4
+; CHECK-NEXT:    ldr r1, [r0]
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r2, #2
+; CHECK-NEXT:    movs r3, #0
+; CHECK-NEXT:    bx r1
   %1 = load i32 (i32, i64)*, i32 (i32, i64)** @fnptr4
   %2 = tail call i32 %1(i32 1, i64 2)
   ret i32 %2
@@ -96,8 +150,12 @@ define i32 @test6() {
 ; tail-call optimized.
 define i32 @test7() {
 ; CHECK-LABEL: test7:
-; CHECK: b bar
-; CHECK-NOT: bl bar
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r1, #2
+; CHECK-NEXT:    movs r2, #3
+; CHECK-NEXT:    movs r3, #4
+; CHECK-NEXT:    b bar
   %tail = tail call i32 @bar(i32 1, i32 2, i32 3, i32 4)
   ret i32 %tail
 }
@@ -109,6 +167,33 @@ declare i32 @bar(i32, i32, i32, i32)
 %struct.S = type { i32 }
 
 define void @test8(i32 (i32, i32, i32)* nocapture %fn, i32 %x) local_unnamed_addr {
+; CHECK-LABEL: test8:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    push {r4, r5, r6, r7, lr}
+; CHECK-NEXT:    sub sp, #4
+; CHECK-NEXT:    mov r4, r1
+; CHECK-NEXT:    str r0, [sp] @ 4-byte Spill
+; CHECK-NEXT:    bl test8_u
+; CHECK-NEXT:    mov r5, r0
+; CHECK-NEXT:    ldr r6, [r0]
+; CHECK-NEXT:    movs r7, #0
+; CHECK-NEXT:    mov r0, r7
+; CHECK-NEXT:    bl test8_h
+; CHECK-NEXT:    mov r1, r0
+; CHECK-NEXT:    mov r0, r6
+; CHECK-NEXT:    mov r2, r7
+; CHECK-NEXT:    bl test8_g
+; CHECK-NEXT:    str r4, [r5]
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    movs r1, #2
+; CHECK-NEXT:    movs r2, #3
+; CHECK-NEXT:    ldr r3, [sp] @ 4-byte Reload
+; CHECK-NEXT:    add sp, #4
+; CHECK-NEXT:    ldr r4, [sp, #16]
+; CHECK-NEXT:    mov lr, r4
+; CHECK-NEXT:    pop {r4, r5, r6, r7}
+; CHECK-NEXT:    add sp, #4
+; CHECK-NEXT:    bx r3
 entry:
   %call = tail call %struct.S* bitcast (%struct.S* (...)* @test8_u to %struct.S* ()*)()
   %a = getelementptr inbounds %struct.S, %struct.S* %call, i32 0, i32 0
@@ -125,6 +210,28 @@ declare %struct.S* @test8_u(...)
 declare i32 @test8_g(i32, i32, i32)
 
 declare i32 @test8_h(i32)
-; CHECK: str r0, [sp] @ 4-byte Spill
-; CHECK: ldr r3, [sp] @ 4-byte Reload
-; CHECK: bx r3
+
+; Check that we don't introduce an unnecessary spill of lr.
+declare i32 @h9(i32, i32, i32, i32)
+define i32 @test9(i32* %x, i32* %y, i32* %z, i32* %a) {
+; CHECK-LABEL: test9:
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    push {r4, r7}
+; CHECK-NEXT:    ldr r4, [r3]
+; CHECK-NEXT:    ldr r3, [r3, #4]
+; CHECK-NEXT:    adds r3, r4, r3
+; CHECK-NEXT:    ldr r1, [r1]
+; CHECK-NEXT:    ldr r0, [r0]
+; CHECK-NEXT:    ldr r2, [r2]
+; CHECK-NEXT:    pop {r4, r7}
+; CHECK-NEXT:    b h9
+  %zz = load i32, i32* %z
+  %xx = load i32, i32* %x
+  %yy = load i32, i32* %y
+  %aa1 = load i32, i32* %a
+  %a2 = getelementptr i32, i32* %a, i32 1
+  %aa2 = load i32, i32* %a2
+  %aa = add i32 %aa1, %aa2
+  %r = tail call i32 @h9(i32 %xx, i32 %yy, i32 %zz, i32 %aa)
+  ret i32 %r
+}