RegisterCoalescer: Fix joinReservedPhysReg()

Merging r294268:

joinReservedPhysReg() can only deal with a liverange in a single basic
block when copying from a vreg into a physreg.

See also rdar://30306405

Differential Revision: https://reviews.llvm.org/D29436

Fixes http://llvm.org/PR31889

llvm-svn: 294631

llvm/lib/CodeGen/RegisterCoalescer.cpp

@@ -1614,6 +1614,11 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
       return false;
     }
 
+    if (!LIS->intervalIsInOneMBB(RHS)) {
+      DEBUG(dbgs() << "\t\tComplex control flow!\n");
+      return false;
+    }
+
     MachineInstr &DestMI = *MRI->getVRegDef(SrcReg);
     CopyMI = &*MRI->use_instr_nodbg_begin(SrcReg);
     SlotIndex CopyRegIdx = LIS->getInstructionIndex(*CopyMI).getRegSlot();

llvm/test/CodeGen/AArch64/regcoal-physreg.mir

@@ -1,19 +1,24 @@
 # RUN: llc -mtriple=aarch64-apple-ios -run-pass=simple-register-coalescing %s -o - | FileCheck %s
 --- |
-  define void @func() { ret void }
+  define void @func0() { ret void }
+  define void @func1() { ret void }
+  define void @func2() { ret void }
 ...
 ---
 # Check coalescing of COPYs from reserved physregs.
-# CHECK-LABEL: name: func
-name: func
+# CHECK-LABEL: name: func0
+name: func0
 registers:
-  - { id: 0, class: gpr32 }
-  - { id: 1, class: gpr64 }
-  - { id: 2, class: gpr64 }
-  - { id: 3, class: gpr32 }
-  - { id: 4, class: gpr64 }
-  - { id: 5, class: gpr32 }
-  - { id: 6, class: xseqpairsclass }
+ - { id: 0, class: gpr32 }
+ - { id: 1, class: gpr64 }
+ - { id: 2, class: gpr64 }
+ - { id: 3, class: gpr32 }
+ - { id: 4, class: gpr64 }
+ - { id: 5, class: gpr32 }
+ - { id: 6, class: xseqpairsclass }
+ - { id: 7, class: gpr64 }
+ - { id: 8, class: gpr64sp }
+ - { id: 9, class: gpr64sp }
 body: |
   bb.0:
     ; We usually should not coalesce copies from allocatable physregs.
@@ -60,8 +65,74 @@ body: |
     ; Only coalesce when the source register is reserved as a whole (this is
     ; a limitation of the current code which cannot update liveness information
     ; of the non-reserved part).
-    ; CHECK: %6 = COPY %xzr_x0
+    ; CHECK: %6 = COPY %x28_fp
     ; CHECK: HINT 0, implicit %6
-    %6 = COPY %xzr_x0
+    %6 = COPY %x28_fp
     HINT 0, implicit %6
+
+    ; This can be coalesced.
+    ; CHECK: %fp = SUBXri %fp, 4, 0
+    %8 = SUBXri %fp, 4, 0
+    %fp = COPY %8
+
+    ; Cannot coalesce when there are reads of the physreg.
+    ; CHECK-NOT: %fp = SUBXri %fp, 8, 0
+    ; CHECK: %9 = SUBXri %fp, 8, 0
+    ; CHECK: STRXui %fp, %fp, 0
+    ; CHECK: %fp = COPY %9
+    %9 = SUBXri %fp, 8, 0
+    STRXui %fp, %fp, 0
+    %fp = COPY %9
+...
+---
+# Check coalescing of COPYs from reserved physregs.
+# CHECK-LABEL: name: func1
+name: func1
+registers:
+ - { id: 0, class: gpr64sp }
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    ; Cannot coalesce physreg because we have reads on other CFG paths (we
+    ; currently abort for any control flow)
+    ; CHECK-NOT: %fp = SUBXri
+    ; CHECK: %0 = SUBXri %fp, 12, 0
+    ; CHECK: CBZX undef %x0, %bb.1
+    ; CHECK: B %bb.2
+    %0 = SUBXri %fp, 12, 0
+    CBZX undef %x0, %bb.1
+    B %bb.2
+
+  bb.1:
+    %fp = COPY %0
+    RET_ReallyLR
+
+  bb.2:
+    STRXui %fp, %fp, 0
+    RET_ReallyLR
+...
+---
+# CHECK-LABEL: name: func2
+name: func2
+registers:
+  - { id: 0, class: gpr64sp }
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    ; We can coalesce copies from physreg to vreg across multiple blocks.
+    ; CHECK-NOT: COPY
+    ; CHECK: CBZX undef %x0, %bb.1
+    ; CHECK-NEXT: B %bb.2
+    %0 = COPY %fp
+    CBZX undef %x0, %bb.1
+    B %bb.2
+
+  bb.1:
+    ; CHECK: STRXui undef %x0, %fp, 0
+    ; CHECK-NEXT: RET_ReallyLR
+    STRXui undef %x0, %0, 0
+    RET_ReallyLR
+
+  bb.2:
+    RET_ReallyLR
 ...