Index: llvm/lib/Target/RISCV/RISCVCodeGenPrepare.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVCodeGenPrepare.cpp
+++ llvm/lib/Target/RISCV/RISCVCodeGenPrepare.cpp
@@ -29,6 +29,8 @@
 #define PASS_NAME "RISCV CodeGenPrepare"
 
 STATISTIC(NumZExtToSExt, "Number of SExt instructions converted to ZExt");
+STATISTIC(NumZExtToSExtNonNeg,
+          "Number of SExt non negative value instructions converted to ZExt");
 
 namespace {
 
@@ -84,6 +86,30 @@
     return true;
   }
 
+  // Look for an non negative zext(value) and replace it with sext.
+  if (isKnownNonNegative(Src, *DL)) {
+    auto SExt = new SExtInst(Src, ZExt.getType(), "", &ZExt);
+    SExt->takeName(&ZExt);
+    SExt->setDebugLoc(ZExt.getDebugLoc());
+
+    ZExt.replaceAllUsesWith(SExt);
+    ZExt.eraseFromParent();
+    ++NumZExtToSExtNonNeg;
+    return true;
+  }
+
+  // Look for zext instructions that can be sext.
+  if (ZExt.wasSext()) {
+    auto SExt = new SExtInst(Src, ZExt.getType(), "", &ZExt);
+    SExt->takeName(&ZExt);
+    SExt->setDebugLoc(ZExt.getDebugLoc());
+
+    ZExt.replaceAllUsesWith(SExt);
+    ZExt.eraseFromParent();
+    ++NumZExtToSExtNonNeg;
+    return true;
+  }
+
   // Convert (zext (abs(i32 X, i1 1))) -> (sext (abs(i32 X, i1 1))). If abs of
   // INT_MIN is poison, the sign bit is zero.
   using namespace PatternMatch;