LowerSwitch: track bounding range for the condition tree.
When LowerSwitch transforms a switch instruction into a tree of ifs it
is actually performing a binary search into the various case ranges, to
see if the current value falls into one cases range of values.
So, if we have a program with something like this:
switch (a) {
case 0:
do0();
break;
case 1:
do1();
break;
case 2:
do2();
break;
default:
break;
}
the code produced is something like this:
if (a < 1) {
if (a == 0) {
do0();
}
} else {
if (a < 2) {
if (a == 1) {
do1();
}
} else {
if (a == 2) {
do2();
}
}
}
This code is inefficient because the check (a == 1) to execute do1() is
not needed.
The reason is that because we already checked that (a >= 1) initially by
checking that also (a < 2) we basically already inferred that (a == 1)
without the need of an extra basic block spawned to check if actually (a
== 1).
The patch addresses this problem by keeping track of already
checked bounds in the LowerSwitch algorithm, so that when the time
arrives to produce a Leaf Block that checks the equality with the case
value / range the algorithm can decide if that block is really needed
depending on the already checked bounds .
For example, the above with "a = 1" would work like this:
the bounds start as LB: NONE , UB: NONE
as (a < 1) is emitted the bounds for the else path become LB: 1 UB:
NONE. This happens because by failing the test (a < 1) we know that the
value "a" cannot be smaller than 1 if we enter the else branch.
After the emitting the check (a < 2) the bounds in the if branch become
LB: 1 UB: 1. This is because by checking that "a" is smaller than 2 then
the upper bound becomes 2 - 1 = 1.
When it is time to emit the leaf block for "case 1:" we notice that 1
can be squeezed exactly in between the LB and UB, which means that if we
arrived to that block there is no need to emit a block that checks if (a
== 1).
Patch by: Marcello Maggioni <hayarms@gmail.com>
llvm-svn: 211038
diff --git a/llvm/test/Transforms/LowerSwitch/feature.ll b/llvm/test/Transforms/LowerSwitch/feature.ll
index e85f03e..09d25f0 100644
--- a/llvm/test/Transforms/LowerSwitch/feature.ll
+++ b/llvm/test/Transforms/LowerSwitch/feature.ll
@@ -3,93 +3,57 @@
; We have switch on input.
; On output we should got binary comparison tree. Check that all is fine.
-;CHECK: entry:
-;CHECK-NEXT: br label %NodeBlock37
+;CHECK: entry:
+;CHECK-NEXT: br label %NodeBlock19
-;CHECK: NodeBlock37: ; preds = %entry
-;CHECK-NEXT: %Pivot38 = icmp slt i32 %tmp158, 10
-;CHECK-NEXT: br i1 %Pivot38, label %NodeBlock13, label %NodeBlock35
+;CHECK: NodeBlock19: ; preds = %entry
+;CHECK-NEXT: %Pivot20 = icmp slt i32 %tmp158, 10
+;CHECK-NEXT: br i1 %Pivot20, label %NodeBlock5, label %NodeBlock17
-;CHECK: NodeBlock35: ; preds = %NodeBlock37
-;CHECK-NEXT: %Pivot36 = icmp slt i32 %tmp158, 13
-;CHECK-NEXT: br i1 %Pivot36, label %NodeBlock23, label %NodeBlock33
+;CHECK: NodeBlock17: ; preds = %NodeBlock19
+;CHECK-NEXT: %Pivot18 = icmp slt i32 %tmp158, 13
+;CHECK-NEXT: br i1 %Pivot18, label %NodeBlock9, label %NodeBlock15
-;CHECK: NodeBlock33: ; preds = %NodeBlock35
-;CHECK-NEXT: %Pivot34 = icmp slt i32 %tmp158, 14
-;CHECK-NEXT: br i1 %Pivot34, label %LeafBlock25, label %NodeBlock31
+;CHECK: NodeBlock15: ; preds = %NodeBlock17
+;CHECK-NEXT: %Pivot16 = icmp slt i32 %tmp158, 14
+;CHECK-NEXT: br i1 %Pivot16, label %bb330, label %NodeBlock13
-;CHECK: NodeBlock31: ; preds = %NodeBlock33
-;CHECK-NEXT: %Pivot32 = icmp slt i32 %tmp158, 15
-;CHECK-NEXT: br i1 %Pivot32, label %LeafBlock27, label %LeafBlock29
+;CHECK: NodeBlock13: ; preds = %NodeBlock15
+;CHECK-NEXT: %Pivot14 = icmp slt i32 %tmp158, 15
+;CHECK-NEXT: br i1 %Pivot14, label %bb332, label %LeafBlock11
-;CHECK: LeafBlock29: ; preds = %NodeBlock31
-;CHECK-NEXT: %SwitchLeaf30 = icmp eq i32 %tmp158, 15
-;CHECK-NEXT: br i1 %SwitchLeaf30, label %bb334, label %NewDefault
+;CHECK: LeafBlock11: ; preds = %NodeBlock13
+;CHECK-NEXT: %SwitchLeaf12 = icmp eq i32 %tmp158, 15
+;CHECK-NEXT: br i1 %SwitchLeaf12, label %bb334, label %NewDefault
-;CHECK: LeafBlock27: ; preds = %NodeBlock31
-;CHECK-NEXT: %SwitchLeaf28 = icmp eq i32 %tmp158, 14
-;CHECK-NEXT: br i1 %SwitchLeaf28, label %bb332, label %NewDefault
+;CHECK: NodeBlock9: ; preds = %NodeBlock17
+;CHECK-NEXT: %Pivot10 = icmp slt i32 %tmp158, 11
+;CHECK-NEXT: br i1 %Pivot10, label %bb324, label %NodeBlock7
-;CHECK: LeafBlock25: ; preds = %NodeBlock33
-;CHECK-NEXT: %SwitchLeaf26 = icmp eq i32 %tmp158, 13
-;CHECK-NEXT: br i1 %SwitchLeaf26, label %bb330, label %NewDefault
+;CHECK: NodeBlock7: ; preds = %NodeBlock9
+;CHECK-NEXT: %Pivot8 = icmp slt i32 %tmp158, 12
+;CHECK-NEXT: br i1 %Pivot8, label %bb326, label %bb328
-;CHECK: NodeBlock23: ; preds = %NodeBlock35
-;CHECK-NEXT: %Pivot24 = icmp slt i32 %tmp158, 11
-;CHECK-NEXT: br i1 %Pivot24, label %LeafBlock15, label %NodeBlock21
+;CHECK: NodeBlock5: ; preds = %NodeBlock19
+;CHECK-NEXT: %Pivot6 = icmp slt i32 %tmp158, 7
+;CHECK-NEXT: br i1 %Pivot6, label %NodeBlock, label %NodeBlock3
-;CHECK: NodeBlock21: ; preds = %NodeBlock23
-;CHECK-NEXT: %Pivot22 = icmp slt i32 %tmp158, 12
-;CHECK-NEXT: br i1 %Pivot22, label %LeafBlock17, label %LeafBlock19
+;CHECK: NodeBlock3: ; preds = %NodeBlock5
+;CHECK-NEXT: %Pivot4 = icmp slt i32 %tmp158, 8
+;CHECK-NEXT: br i1 %Pivot4, label %bb, label %NodeBlock1
-;CHECK: LeafBlock19: ; preds = %NodeBlock21
-;CHECK-NEXT: %SwitchLeaf20 = icmp eq i32 %tmp158, 12
-;CHECK-NEXT: br i1 %SwitchLeaf20, label %bb328, label %NewDefault
+;CHECK: NodeBlock1: ; preds = %NodeBlock3
+;CHECK-NEXT: %Pivot2 = icmp slt i32 %tmp158, 9
+;CHECK-NEXT: br i1 %Pivot2, label %bb338, label %bb322
-;CHECK: LeafBlock17: ; preds = %NodeBlock21
-;CHECK-NEXT: %SwitchLeaf18 = icmp eq i32 %tmp158, 11
-;CHECK-NEXT: br i1 %SwitchLeaf18, label %bb326, label %NewDefault
+;CHECK: NodeBlock: ; preds = %NodeBlock5
+;CHECK-NEXT: %Pivot = icmp slt i32 %tmp158, 0
+;CHECK-NEXT: br i1 %Pivot, label %LeafBlock, label %bb338
-;CHECK: LeafBlock15: ; preds = %NodeBlock23
-;CHECK-NEXT: %SwitchLeaf16 = icmp eq i32 %tmp158, 10
-;CHECK-NEXT: br i1 %SwitchLeaf16, label %bb324, label %NewDefault
-
-;CHECK: NodeBlock13: ; preds = %NodeBlock37
-;CHECK-NEXT: %Pivot14 = icmp slt i32 %tmp158, 7
-;CHECK-NEXT: br i1 %Pivot14, label %NodeBlock, label %NodeBlock11
-
-;CHECK: NodeBlock11: ; preds = %NodeBlock13
-;CHECK-NEXT: %Pivot12 = icmp slt i32 %tmp158, 8
-;CHECK-NEXT: br i1 %Pivot12, label %LeafBlock3, label %NodeBlock9
-
-;CHECK: NodeBlock9: ; preds = %NodeBlock11
-;CHECK-NEXT: %Pivot10 = icmp slt i32 %tmp158, 9
-;CHECK-NEXT: br i1 %Pivot10, label %LeafBlock5, label %LeafBlock7
-
-;CHECK: LeafBlock7: ; preds = %NodeBlock9
-;CHECK-NEXT: %SwitchLeaf8 = icmp eq i32 %tmp158, 9
-;CHECK-NEXT: br i1 %SwitchLeaf8, label %bb322, label %NewDefault
-
-;CHECK: LeafBlock5: ; preds = %NodeBlock9
-;CHECK-NEXT: %SwitchLeaf6 = icmp eq i32 %tmp158, 8
-;CHECK-NEXT: br i1 %SwitchLeaf6, label %bb338, label %NewDefault
-
-;CHECK: LeafBlock3: ; preds = %NodeBlock11
-;CHECK-NEXT: %SwitchLeaf4 = icmp eq i32 %tmp158, 7
-;CHECK-NEXT: br i1 %SwitchLeaf4, label %bb, label %NewDefault
-
-;CHECK: NodeBlock: ; preds = %NodeBlock13
-;CHECK-NEXT: %Pivot = icmp slt i32 %tmp158, 0
-;CHECK-NEXT: br i1 %Pivot, label %LeafBlock, label %LeafBlock1
-
-;CHECK: LeafBlock1: ; preds = %NodeBlock
-;CHECK-NEXT: %SwitchLeaf2 = icmp ule i32 %tmp158, 6
-;CHECK-NEXT: br i1 %SwitchLeaf2, label %bb338, label %NewDefault
-
-;CHECK: LeafBlock: ; preds = %NodeBlock
-;CHECK-NEXT: %tmp158.off = add i32 %tmp158, 6
-;CHECK-NEXT: %SwitchLeaf = icmp ule i32 %tmp158.off, 4
-;CHECK-NEXT: br i1 %SwitchLeaf, label %bb338, label %NewDefault
+;CHECK: LeafBlock: ; preds = %NodeBlock
+;CHECK-NEXT: %tmp158.off = add i32 %tmp158, 6
+;CHECK-NEXT: %SwitchLeaf = icmp ule i32 %tmp158.off, 4
+;CHECK-NEXT: br i1 %SwitchLeaf, label %bb338, label %NewDefault
define i32 @main(i32 %tmp158) {
entry: