[AArch64][GlobalISel] Make G_PHI of p0 types legal

[aemerson]

Summary

Make G_PHI of p0 types legal.

These seem to contribute a significant proportion of the SDAG bailouts on a test suite build.

[aemerson]

Forgot to add llvm-commits.

[qcolombet]

Hi Amara,

LGTM.

Could you add checks (in follow on commits) for both regbankselect and instruction select passes to make sure G_PHIs with p0 pass those two as well?

Cheers,
-Quentin

[aemerson]

Thanks, will do.

lib/Target/AArch64/AArch64LegalizerInfo.cpp

AArch64LegalizerInfo::AArch64LegalizerInfo() {
   const LLT s64 = LLT::scalar(64);
   const LLT v2s32 = LLT::vector(2, 32);
   const LLT v4s32 = LLT::vector(4, 32);
   const LLT v2s64 = LLT::vector(2, 64);
 
   for (auto Ty : {p0, s1, s8, s16, s32, s64})
     setAction({G_IMPLICIT_DEF, Ty}, Legal);
 
-  for (auto Ty : {s16, s32, s64})
+  for (auto Ty : {s16, s32, s64, p0})
     setAction({G_PHI, Ty}, Legal);
 
   for (auto Ty : {s1, s8})
     setAction({G_PHI, Ty}, WidenScalar);
 
   for (auto Ty : { s32, s64 })
     setAction({G_BSWAP, Ty}, Legal);
 

test/CodeGen/AArch64/GlobalISel/legalize-phi.mir

 # RUN: llc -mtriple=aarch64-unknown-unknown -global-isel -verify-machineinstrs -run-pass=legalizer %s -o - | FileCheck %s
 --- |
   ; ModuleID = '/tmp/test.ll'
   source_filename = "/tmp/test.ll"
   target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
   target triple = "aarch64-unknown-unknown"
   
   define i32 @legalize_phi(i32 %argc) {
   entry:
     ret i32 0
   }
 
+  define i64* @legalize_phi_ptr(i64* %a, i64* %b, i1 %cond) {
+  entry:
+    ret i64* null
+  }
+
   define i32 @legalize_phi_empty(i32 %argc) {
   entry:
     ret i32 0
   }
 
   define i32 @legalize_phi_loop(i32 %argc) {
   entry:
     ret i32 0
body:             |
   bb.3:
     %9(s1) = G_PHI %5(s1), %bb.1, %8(s1), %bb.2
     %10(s32) = G_ZEXT %9(s1)
     %w0 = COPY %10(s32)
     RET_ReallyLR implicit %w0
 
 ...
 ---
+name:            legalize_phi_ptr
+alignment:       2
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+  - { id: 1, class: _, preferred-register: '' }
+  - { id: 2, class: _, preferred-register: '' }
+  - { id: 3, class: _, preferred-register: '' }
+  - { id: 4, class: _, preferred-register: '' }
+  - { id: 5, class: _, preferred-register: '' }
+liveins:
+body:             |
+  bb.1:
+   ; CHECK-LABEL: name: legalize_phi_ptr
+   ; CHECK-LABEL: bb.0:
+   ; CHECK: %0(p0) = COPY %x0
+   ; CHECK: %1(p0) = COPY %x1
+   ; CHECK: %2(s1) = COPY %w2
+
+   ; CHECK-LABEL: bb.1:
+   ; CHECK-LABEL: bb.2:
+   ; CHECK: %3(p0) = G_PHI %0(p0), %bb.0, %1(p0), %bb.1
+   ; CHECK: %x0 = COPY %3(p0)
+    successors: %bb.2, %bb.3
+    liveins: %w2, %x0, %x1
+
+    %0(p0) = COPY %x0
+    %1(p0) = COPY %x1
+    %2(s1) = COPY %w2
+    G_BRCOND %2(s1), %bb.2
+    G_BR %bb.3
+
+  bb.2:
+    successors: %bb.3
+
+  bb.3:
+    %3(p0) = G_PHI %0(p0), %bb.1, %1(p0), %bb.2
+    %x0 = COPY %3(p0)
+    RET_ReallyLR implicit %x0
+
+...
+---
 name:            legalize_phi_empty
 alignment:       2
 exposesReturnsTwice: false
 legalized:       false
 regBankSelected: false
 selected:        false
 tracksRegLiveness: true
 registers: