[ARM] Don't replicate instructions in Ifcvt at minsize

Ifcvt can replicate instructions as it converts them to be predicated. This
stops that from happening on thumb2 targets at minsize where an extra IT
instruction is likely needed.

Differential Revision: https://reviews.llvm.org/D60089

llvm-svn: 358974

llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp

@@ -1933,6 +1933,15 @@ isProfitableToIfCvt(MachineBasicBlock &TBB,
   if (!TCycles)
     return false;
 
+  // In thumb code we often end up trading one branch for a IT block, and
+  // if we are cloning the instruction can increase code size. Prevent
+  // blocks with multiple predecesors from being ifcvted to prevent this
+  // cloning.
+  if (Subtarget.isThumb2() && TBB.getParent()->getFunction().hasMinSize()) {
+    if (TBB.pred_size() != 1 || FBB.pred_size() != 1)
+      return false;
+  }
+
   // Attempt to estimate the relative costs of predication versus branching.
   // Here we scale up each component of UnpredCost to avoid precision issue when
   // scaling TCycles/FCycles by Probability.

llvm/test/CodeGen/Thumb2/ifcvt-minsize.ll

@@ -0,0 +1,92 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=thumbv8m.main-none-none-eabi %s -o - -verify-machineinstrs | FileCheck %s
+
+declare i32 @fn(i32) #0
+
+define i32 @f1(i32 %a) #0 {
+; CHECK-LABEL: f1:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r4, lr}
+; CHECK-NEXT:    push {r4, lr}
+; CHECK-NEXT:    mov r4, r0
+; CHECK-NEXT:    bl fn
+; CHECK-NEXT:    movs r0, #0
+; CHECK-NEXT:    cbz r4, .LBB0_2
+; CHECK-NEXT:  @ %bb.1: @ %return
+; CHECK-NEXT:    pop {r4, pc}
+; CHECK-NEXT:  .LBB0_2: @ %if.end
+; CHECK-NEXT:    bl fn
+; CHECK-NEXT:    adds r0, #1
+; CHECK-NEXT:    pop {r4, pc}
+entry:
+  %call = tail call i32 @fn(i32 %a) #2
+  %tobool = icmp eq i32 %a, 0
+  br i1 %tobool, label %if.end, label %return
+
+if.end:                                           ; preds = %entry
+  %call1 = tail call i32 @fn(i32 0) #2
+  %add = add nsw i32 %call1, 1
+  br label %return
+
+return:                                           ; preds = %entry, %if.end
+  %retval.0 = phi i32 [ %add, %if.end ], [ 0, %entry ]
+  ret i32 %retval.0
+}
+
+define i32 @f2(i32 %a) #0 {
+; CHECK-LABEL: f2:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r4, lr}
+; CHECK-NEXT:    push {r4, lr}
+; CHECK-NEXT:    mov r4, r0
+; CHECK-NEXT:    bl fn
+; CHECK-NEXT:    movs r0, #0
+; CHECK-NEXT:    cmp r4, #1
+; CHECK-NEXT:    bne .LBB1_2
+; CHECK-NEXT:  @ %bb.1: @ %if.end
+; CHECK-NEXT:    bl fn
+; CHECK-NEXT:    adds r0, #1
+; CHECK-NEXT:  .LBB1_2: @ %return
+; CHECK-NEXT:    pop {r4, pc}
+entry:
+  %call = tail call i32 @fn(i32 %a) #2
+  %tobool = icmp eq i32 %a, 1
+  br i1 %tobool, label %if.end, label %return
+
+if.end:                                           ; preds = %entry
+  %call1 = tail call i32 @fn(i32 0) #2
+  %add = add nsw i32 %call1, 1
+  br label %return
+
+return:                                           ; preds = %entry, %if.end
+  %retval.0 = phi i32 [ %add, %if.end ], [ 0, %entry ]
+  ret i32 %retval.0
+}
+
+define void @f3(i32 %x) #0 {
+; CHECK-LABEL: f3:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    cmp r0, #1
+; CHECK-NEXT:    bne .LBB2_2
+; CHECK-NEXT:  @ %bb.1: @ %t
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    movs r0, #0
+; CHECK-NEXT:    bl fn
+; CHECK-NEXT:    pop.w {r7, lr}
+; CHECK-NEXT:  .LBB2_2: @ %f
+; CHECK-NEXT:    bx lr
+entry:
+  %p = icmp eq i32 %x, 1
+  br i1 %p, label %t, label %f
+
+t:
+  call i32 @fn(i32 0)
+  br label %f
+
+f:
+  ret void
+}
+
+attributes #0 = { minsize nounwind optsize }
+