[AArch64][Redundant Copy Elim] Add support for CMN and shifted imm.

This patch extends the current functionality of the AArch64 redundant copy
elimination pass to handle CMN instructions as well as a shifted
immediates.

Differential Revision: https://reviews.llvm.org/D30576.

llvm-svn: 297078

2 files changed, 148 insertions, 6 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp b/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp
index a935d39ccfd..f3c8e7e9bdc 100644
--- a/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp
+++ b/llvm/lib/Target/AArch64/AArch64RedundantCopyElimination.cpp
@@ -154,30 +154,37 @@ AArch64RedundantCopyElimination::knownRegValInBlock(
     // Track clobbered registers.
     trackRegDefs(PredI, ClobberedRegs, TRI);
 
+    bool IsCMN = false;
     switch (PredI.getOpcode()) {
     default:
       break;
 
+    // CMN is an alias for ADDS with a dead destination register.
+    case AArch64::ADDSWri:
+    case AArch64::ADDSXri:
+      IsCMN = true;
     // CMP is an alias for SUBS with a dead destination register.
     case AArch64::SUBSWri:
     case AArch64::SUBSXri: {
-      unsigned SrcReg = PredI.getOperand(1).getReg();
+      MCPhysReg SrcReg = PredI.getOperand(1).getReg();
+
       // Must not be a symbolic immediate.
       if (!PredI.getOperand(2).isImm())
         return None;
 
-      // FIXME: For simplicity, give up on non-zero shifts.
-      if (PredI.getOperand(3).getImm())
-        return None;
-
       // The src register must not be modified between the cmp and conditional
       // branch.  This includes a self-clobbering compare.
       if (ClobberedRegs[SrcReg])
         return None;
 
       // We've found the Cmp that sets NZCV.
+      int32_t KnownImm = PredI.getOperand(2).getImm();
+      int32_t Shift = PredI.getOperand(3).getImm();
+      KnownImm <<= Shift;
+      if (IsCMN)
+        KnownImm = -KnownImm;
       FirstUse = PredI;
-      return RegImm(PredI.getOperand(1).getReg(), PredI.getOperand(2).getImm());
+      return RegImm(SrcReg, KnownImm);
     }
     }
 
diff --git a/llvm/test/CodeGen/AArch64/machine-copy-remove.mir b/llvm/test/CodeGen/AArch64/machine-copy-remove.mir
index 56400ba9d74..6f2d3a3009b 100644
--- a/llvm/test/CodeGen/AArch64/machine-copy-remove.mir
+++ b/llvm/test/CodeGen/AArch64/machine-copy-remove.mir
@@ -535,3 +535,138 @@ body:             |
 
   bb.2:
     RET_ReallyLR
+...
+# Eliminate redundant MOVi32imm -1 in bb.1
+# Note: 32-bit compare/32-bit move imm
+# Kill marker should be removed from compare.
+# CHECK-LABEL: name: test19
+# CHECK: ADDSWri %w0, 1, 0, implicit-def %nzcv
+# CHECK: bb.1:
+# CHECK-NOT: MOVi32imm
+name:            test19
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    successors: %bb.1, %bb.2
+    liveins: %w0, %x1
+
+    dead %wzr = ADDSWri killed %w0, 1, 0, implicit-def %nzcv
+    Bcc 1, %bb.2, implicit killed %nzcv
+    B %bb.1
+
+  bb.1:
+    successors: %bb.2
+    liveins: %x1
+
+    %w0 = MOVi32imm -1
+    STRWui killed %w0, killed %x1, 0
+
+  bb.2:
+    RET_ReallyLR
+...
+# Eliminate redundant MOVi64imm -1 in bb.1
+# Note: 64-bit compare/64-bit move imm
+# Kill marker should be removed from compare.
+# CHECK-LABEL: name: test20
+# CHECK: ADDSXri %x0, 1, 0, implicit-def %nzcv
+# CHECK: bb.1:
+# CHECK-NOT: MOVi64imm
+name:            test20
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.1, %bb.2
+    liveins: %x0, %x1
+
+    dead %xzr = ADDSXri killed %x0, 1, 0, implicit-def %nzcv
+    Bcc 1, %bb.2, implicit killed %nzcv
+    B %bb.1
+
+  bb.1:
+    successors: %bb.2
+    liveins: %x1
+
+    %x0 = MOVi64imm -1
+    STRXui killed %x0, killed %x1, 0
+
+  bb.2:
+    RET_ReallyLR
+...
+# Eliminate redundant MOVi32imm -1 in bb.1
+# Note: 64-bit compare/32-bit move imm
+# Kill marker should be removed from compare.
+# CHECK-LABEL: name: test21
+# CHECK: ADDSXri %x0, 1, 0, implicit-def %nzcv
+# CHECK: bb.1:
+# CHECK-NOT: MOVi32imm
+name:            test21
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    successors: %bb.1, %bb.2
+    liveins: %x0, %x1
+
+    dead %xzr = ADDSXri killed %x0, 1, 0, implicit-def %nzcv
+    Bcc 1, %bb.2, implicit killed %nzcv
+    B %bb.1
+
+  bb.1:
+    successors: %bb.2
+    liveins: %x1
+
+    %w0 = MOVi32imm -1
+    STRWui killed %w0, killed %x1, 0
+
+  bb.2:
+    RET_ReallyLR
+...
+# Don't eliminate MOVi64imm -1 in bb.1 as we don't necessarily know the upper 32-bits.
+# Note: 32-bit compare/64-bit move imm
+# CHECK-LABEL: name: test22
+# CHECK: bb.1:
+# CHECK: MOVi64imm
+name:            test22
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    successors: %bb.1, %bb.2
+    liveins: %w0, %x1
+
+    dead %wzr = ADDSWri killed %w0, 1, 0, implicit-def %nzcv
+    Bcc 1, %bb.2, implicit killed %nzcv
+    B %bb.1
+
+  bb.1:
+    successors: %bb.2
+    liveins: %x1
+
+    %x0 = MOVi64imm -1
+    STRXui killed %x0, killed %x1, 0
+
+  bb.2:
+    RET_ReallyLR
+...
+# Eliminate redundant MOVi32imm 4096 in bb.1 when the compare has a shifted immediate.
+# CHECK-LABEL: name: test23
+# CHECK: bb.1:
+# CHECK-NOT: MOVi32imm
+name:            test23
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    successors: %bb.1, %bb.2
+    liveins: %w0, %x1
+
+    dead %wzr = SUBSWri killed %w0, 1, 12, implicit-def %nzcv
+    Bcc 1, %bb.2, implicit killed %nzcv
+    B %bb.1
+
+  bb.1:
+    successors: %bb.2
+    liveins: %x1
+
+    %w0 = MOVi32imm 4096
+    STRWui killed %w0, killed %x1, 0
+
+  bb.2:
+    RET_ReallyLR