LoopVectorizer: Add support for if-conversion of PHINodes with 3+ incoming values.

By supporting the vectorization of PHINodes with more than two incoming values we can increase the complexity of nested if statements.

We can now vectorize this loop:

int foo(int *A, int *B, int n) {
  for (int i=0; i < n; i++) {
    int x = 9;
    if (A[i] > B[i]) {
      if (A[i] > 19) {
        x = 3;
      } else if (B[i] < 4 ) {
        x = 4;
      } else {
        x = 5;
      }
    }
    A[i] = x;
  }
}



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181037 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 48 insertions, 0 deletions

diff --git a/test/Transforms/LoopVectorize/if-conversion-nest.ll b/test/Transforms/LoopVectorize/if-conversion-nest.ll
new file mode 100644
index 0000000..f44862a
--- /dev/null
+++ b/test/Transforms/LoopVectorize/if-conversion-nest.ll
@@ -0,0 +1,48 @@
+; RUN: opt < %s  -loop-vectorize -force-vector-unroll=1 -force-vector-width=4 -enable-if-conversion -dce -instcombine -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+;CHECK: @foo
+;CHECK: icmp sgt
+;CHECK: icmp sgt
+;CHECK: icmp slt
+;CHECK: select <4 x i1>
+;CHECK: %[[P1:.*]] = select <4 x i1>
+;CHECK: xor <4 x i1>
+;CHECK: and <4 x i1>
+;CHECK: select <4 x i1> %{{.*}}, <4 x i32> %{{.*}}, <4 x i32> %[[P1]]
+;CHECK: ret
+define i32 @foo(i32* nocapture %A, i32* nocapture %B, i32 %n) {
+entry:
+  %cmp26 = icmp sgt i32 %n, 0
+  br i1 %cmp26, label %for.body, label %for.end
+
+for.body:
+  %indvars.iv = phi i64 [ %indvars.iv.next, %if.end14 ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32* %A, i64 %indvars.iv
+  %0 = load i32* %arrayidx, align 4
+  %arrayidx2 = getelementptr inbounds i32* %B, i64 %indvars.iv
+  %1 = load i32* %arrayidx2, align 4
+  %cmp3 = icmp sgt i32 %0, %1
+  br i1 %cmp3, label %if.then, label %if.end14
+
+if.then:
+  %cmp6 = icmp sgt i32 %0, 19
+  br i1 %cmp6, label %if.end14, label %if.else
+
+if.else:
+  %cmp10 = icmp slt i32 %1, 4
+  %. = select i1 %cmp10, i32 4, i32 5
+  br label %if.end14
+
+if.end14:
+  %x.0 = phi i32 [ 9, %for.body ], [ 3, %if.then ], [ %., %if.else ]  ; <------------- A PHI with 3 entries that we can still vectorize.
+  store i32 %x.0, i32* %arrayidx, align 4
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:
+  ret i32 undef
+}