[llvm-commits] [llvm] r166409 - in /llvm/trunk: lib/Transforms/Vectorize/LoopVectorize.cpp test/Transforms/LoopVectorize/scalar-select.ll

[Nadav Rotem]

Author: nadav
Date: Sun Oct 21 23:38:00 2012
New Revision: 166409

URL: http://llvm.org/viewvc/llvm-project?rev=166409&view=rev
Log:
Vectorizer: optimize the generation of selects. If the condition is uniform, generate a scalar-cond select (i1 as selector).

Added:
    llvm/trunk/test/Transforms/LoopVectorize/scalar-select.ll
Modified:
    llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=166409&r1=166408&r2=166409&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Sun Oct 21 23:38:00 2012
@@ -725,12 +725,22 @@
       }
       case Instruction::Select: {
         // Widen selects.
-        // TODO: If the selector is loop invariant we can issue a select
-        // instruction with a scalar condition.
-        Value *A = getVectorValue(Inst->getOperand(0));
-        Value *B = getVectorValue(Inst->getOperand(1));
-        Value *C = getVectorValue(Inst->getOperand(2));
-        WidenMap[Inst] = Builder.CreateSelect(A, B, C);
+        // If the selector is loop invariant we can create a select
+        // instruction with a scalar condition. Otherwise, use vector-select.
+        Value *Cond = Inst->getOperand(0);
+        bool InvariantCond = SE->isLoopInvariant(SE->getSCEV(Cond), Orig);
+
+        // The condition can be loop invariant  but still defined inside the
+        // loop. This means that we can't just use the original 'cond' value.
+        // We have to take the 'vectorized' value and pick the first lane.
+        // Instcombine will make this a no-op.
+        Cond = getVectorValue(Cond);
+        if (InvariantCond)
+          Cond = Builder.CreateExtractElement(Cond, Builder.getInt32(0));
+
+        Value *Op0 = getVectorValue(Inst->getOperand(1));
+        Value *Op1 = getVectorValue(Inst->getOperand(2));
+        WidenMap[Inst] = Builder.CreateSelect(Cond, Op0, Op1);
         break;
       }
 

Added: llvm/trunk/test/Transforms/LoopVectorize/scalar-select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/scalar-select.ll?rev=166409&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/scalar-select.ll (added)
+++ llvm/trunk/test/Transforms/LoopVectorize/scalar-select.ll Sun Oct 21 23:38:00 2012
@@ -0,0 +1,37 @@
+; RUN: opt < %s  -loop-vectorize -dce -instcombine -licm -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"
+target triple = "x86_64-apple-macosx10.8.0"
+
+ at a = common global [2048 x i32] zeroinitializer, align 16
+ at b = common global [2048 x i32] zeroinitializer, align 16
+ at c = common global [2048 x i32] zeroinitializer, align 16
+
+;CHECK: @example1
+;CHECK: load <4 x i32>
+; make sure that we have a scalar condition and a vector operand.
+;CHECK: select i1 %cond, <4 x i32>
+;CHECK: store <4 x i32>
+;CHECK: ret void
+define void @example1(i1 %cond) nounwind uwtable ssp {
+  br label %1
+
+; <label>:1                                       ; preds = %1, %0
+  %indvars.iv = phi i64 [ 0, %0 ], [ %indvars.iv.next, %1 ]
+  %2 = getelementptr inbounds [2048 x i32]* @b, i64 0, i64 %indvars.iv
+  %3 = load i32* %2, align 4
+  %4 = getelementptr inbounds [2048 x i32]* @c, i64 0, i64 %indvars.iv
+  %5 = load i32* %4, align 4
+  %6 = add nsw i32 %5, %3
+  %7 = getelementptr inbounds [2048 x i32]* @a, i64 0, i64 %indvars.iv
+  %sel = select i1 %cond, i32 %6, i32 zeroinitializer
+  store i32 %sel, i32* %7, 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, 256
+  br i1 %exitcond, label %8, label %1
+
+; <label>:8                                       ; preds = %1
+  ret void
+}
+