If-conversion incorrectly calculates liveness of redefined registers

Differential Revision: https://reviews.llvm.org/D23207


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278383 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/IfConversion.cpp

@@ -1689,10 +1689,15 @@ bool IfConverter::IfConvertDiamondCommon(
   // Remove the conditional branch from entry to the blocks.
   BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
 
-  // Initialize liveins to the first BB. These are potentially redefined by
-  // predicated instructions.
+  // Initialize the Redefs:
+  // - BB2 live-in regs need implicit uses before being redefined by BB1
+  //   instructions.
+  // - BB1 live-out regs need implicit uses before being redefined by BB2
+  //   instructions. We start with BB1 live-ins so we have the live-out regs
+  //   after tracking the BB1 instructions.
   Redefs.init(TRI);
   Redefs.addLiveIns(*BBI1->BB);
+  Redefs.addLiveIns(*BBI2->BB);
 
   // Remove the duplicated instructions at the beginnings of both paths.
   // Skip dbg_value instructions

test/CodeGen/Hexagon/ifcvt-impuse-livein.mir

@@ -0,0 +1,43 @@
+# RUN: llc -march=hexagon -run-pass if-converter %s -o - | FileCheck %s
+
+# Make sure that the necessary implicit uses are added to predicated
+# instructions.
+
+# CHECK-LABEL: name: foo
+
+--- |
+  define void @foo() {
+    ret void
+  }
+...
+
+---
+name: foo
+tracksRegLiveness: true
+allVRegsAllocated: true
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    liveins: %r0, %r2, %p1
+        J2_jumpf %p1, %bb.1, implicit-def %pc
+        J2_jump %bb.2, implicit-def %pc
+  bb.1:
+    successors: %bb.3
+    liveins: %r2
+        %r0 = A2_tfrsi 2
+        J2_jump %bb.3, implicit-def %pc
+  bb.2:
+    successors: %bb.3
+    liveins: %r0
+    ; Even though r2 was not live on entry to this block, it was live across
+    ; block bb.1 in the original diamond. After if-conversion, the diamond
+    ; became a single block, and so r2 is now live on entry to the instructions
+    ; originating from bb.2.
+    ; CHECK: %r2 = C2_cmoveit %p1, 1, implicit %r2
+        %r2 = A2_tfrsi 1
+  bb.3:
+    liveins: %r0, %r2
+        %r0 = A2_add %r0, %r2
+        J2_jumpr %r31, implicit-def %pc
+...
+