From 43de17872a4fce7ad7d41966355d7bd9c4f4f6e6 Mon Sep 17 00:00:00 2001
From: Tobias Grosser <tobias@grosser.es>
Date: Sun, 12 Jun 2016 04:49:41 +0000
Subject: [PATCH] Recommit: "Simplify min/max expression generation"

As part of this simplification we pull complex logic out of the loop body and
skip the previously redundantly executed first loop iteration.

This is a partial recommit of r271514 and r271535 which where in conflict with
the revert in r272483 and consequently also had to be reverted temporarily.  The
original patch was contributed by Johannes Doerfert.

This patch is mostly a NFC, but dropping the first loop iteration can sometimes
result in slightly simpler code.

llvm-svn: 272502
---
 polly/lib/CodeGen/IslExprBuilder.cpp | 37 ++++++++++++----------------
 1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/polly/lib/CodeGen/IslExprBuilder.cpp b/polly/lib/CodeGen/IslExprBuilder.cpp
index 62c166f7b666..e7f8de2ba0df 100644
--- a/polly/lib/CodeGen/IslExprBuilder.cpp
+++ b/polly/lib/CodeGen/IslExprBuilder.cpp
@@ -171,14 +171,22 @@ Value *IslExprBuilder::createOpNAry(__isl_take isl_ast_expr *Expr) {
   assert(isl_ast_expr_get_op_n_arg(Expr) >= 2 &&
          "We need at least two operands in an n-ary operation");
 
-  Value *V;
+  CmpInst::Predicate Pred;
+  switch (isl_ast_expr_get_op_type(Expr)) {
+  default:
+    llvm_unreachable("This is not a an n-ary isl ast expression");
+  case isl_ast_op_max:
+    Pred = CmpInst::ICMP_SGT;
+    break;
+  case isl_ast_op_min:
+    Pred = CmpInst::ICMP_SLT;
+    break;
+  }
 
-  V = create(isl_ast_expr_get_op_arg(Expr, 0));
-
-  for (int i = 0; i < isl_ast_expr_get_op_n_arg(Expr); ++i) {
-    Value *OpV;
-    OpV = create(isl_ast_expr_get_op_arg(Expr, i));
+  Value *V = create(isl_ast_expr_get_op_arg(Expr, 0));
 
+  for (int i = 1; i < isl_ast_expr_get_op_n_arg(Expr); ++i) {
+    Value *OpV = create(isl_ast_expr_get_op_arg(Expr, i));
     Type *Ty = getWidestType(V->getType(), OpV->getType());
 
     if (Ty != OpV->getType())
@@ -187,21 +195,8 @@ Value *IslExprBuilder::createOpNAry(__isl_take isl_ast_expr *Expr) {
     if (Ty != V->getType())
       V = Builder.CreateSExt(V, Ty);
 
-    switch (isl_ast_expr_get_op_type(Expr)) {
-    default:
-      llvm_unreachable("This is no n-ary isl ast expression");
-
-    case isl_ast_op_max: {
-      Value *Cmp = Builder.CreateICmpSGT(V, OpV);
-      V = Builder.CreateSelect(Cmp, V, OpV);
-      continue;
-    }
-    case isl_ast_op_min: {
-      Value *Cmp = Builder.CreateICmpSLT(V, OpV);
-      V = Builder.CreateSelect(Cmp, V, OpV);
-      continue;
-    }
-    }
+    Value *Cmp = Builder.CreateICmp(Pred, V, OpV);
+    V = Builder.CreateSelect(Cmp, V, OpV);
   }
 
   // TODO: We can truncate the result, if it fits into a smaller type. This can