diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1367,6 +1367,13 @@
   return nullptr;
 }
 
+bool phiAllConstantOperandsAreZero(PHINode &PN) {
+  for (Value *V : PN.operands())
+    if (Constant *ConstVA = dyn_cast<Constant>(V))
+      if (!ConstVA->isZeroValue())
+        return false;
+  return true;
+}
 // PHINode simplification
 //
 Instruction *InstCombinerImpl::visitPHINode(PHINode &PN) {
@@ -1465,6 +1472,23 @@
         return &PN;
     }
   }
+  if (phiAllConstantOperandsAreZero(PN)) {
+    for (Value *Operands : PN.operands()) {
+      if (Instruction *Fmul = dyn_cast<Instruction>(Operands)) {
+        if (Fmul->getOpcode() == Instruction::FMul && Fmul->hasNoInfs() &&
+            Fmul->hasNoNaNs() && Fmul->hasNoSignedZeros()) {
+          for (Value *InstOperand : Fmul->operands()) {
+            if (PHINode *PhiOperand = dyn_cast<PHINode>(InstOperand)) {
+              if (PhiOperand == &PN) {
+                auto *ZeroVal = Constant::getNullValue(PN.getType());
+                replaceInstUsesWith(PN, ZeroVal);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
 
   // We sometimes end up with phi cycles that non-obviously end up being the
   // same value, for example:
diff --git a/llvm/test/Transforms/InstCombine/remove-loop-phi-fastmul.ll b/llvm/test/Transforms/InstCombine/remove-loop-phi-fastmul.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/remove-loop-phi-fastmul.ll
@@ -0,0 +1,130 @@
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define double @test_mul_fast_flags() {
+entry:
+  %arr_d = alloca [1000 x double], align 8
+  br label %for.cond
+
+; CHECK-LABEL: for.cond:
+; CHECK-NOT: [[PHI_1:%.*]] = phi double [ 0.000000e+00, [[ENTRY_1:%.*]] ], [ [[MUL_1:%.*]] [[LOOPBODY_1:%.*]] ]
+; CHECK-NEXT: [[PHI_2:%.*]] = phi i64 [ 0, [[ENTRY_2:%.*]] ], [ [[INC_1:%.*]] [[LOOPBODY_2:%.*]] ]
+for.cond:
+  %f_prod.0 = phi double [0.000000e+00, %entry], [%mul, %for.body]
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp ult i64 %i.0, 1000
+  br i1 %cmp, label %for.body, label %end
+
+end:
+  ret double %f_prod.0
+
+for.body:
+  %arrayidx = getelementptr inbounds [1000 x double], ptr %arr_d, i64 0, i64 %i.0
+  %0 = load double, ptr %arrayidx, align 8
+  %mul = fmul fast double %f_prod.0, %0
+  %inc = add i64 %i.0, 1
+  br label %for.cond
+
+}
+
+define double @test_phi_nnan_flag_enabled() {
+entry:
+  %arr_d = alloca [1000 x double], align 8
+  br label %for.cond
+
+; CHECK-LABEL: for.cond:
+; CHECK: [[PHI_3:%.*]] = phi double [ 0.000000e+00, [[ENTRY_3:%.*]] ], [ [[MUL_2:%.*]] [[LOOPBODY_3:%.*]] ]
+; CHECK-NEXT: [[PHI_4:%.*]] = phi i64 [ 0, [[ENTRY_4:%.*]] ], [ [[INC_2:%.*]] [[LOOPBODY_4:%.*]] ]
+for.cond:
+  %f_prod.0 = phi double [0.000000e+00, %entry], [%mul, %for.body]
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp ult i64 %i.0, 1000
+  br i1 %cmp, label %for.body, label %end
+
+end:
+  ret double %f_prod.0
+
+for.body:
+  %arrayidx = getelementptr inbounds [1000 x double], ptr %arr_d, i64 0, i64 %i.0
+  %0 = load double, ptr %arrayidx, align 8
+  %mul = fmul nnan double %f_prod.0, %0
+  %inc = add i64 %i.0, 1
+  br label %for.cond
+
+}
+
+define double @test_phi_ninf_flag_enabled() {
+entry:
+  %arr_d = alloca [1000 x double], align 8
+  br label %for.cond
+
+; CHECK-LABEL: for.cond:
+; CHECK: [[PHI_5:%.*]] = phi double [ 0.000000e+00, [[ENTRY_5:%.*]] ], [ [[MUL_3:%.*]] [[LOOPBODY_5:%.*]] ]
+; CHECK-NEXT: [[PHI_6:%.*]] = phi i64 [ 0, [[ENTRY_6:%.*]] ], [ [[INC_3:%.*]] [[LOOPBODY_6:%.*]] ]
+for.cond:
+  %f_prod.0 = phi double [0.000000e+00, %entry], [%mul, %for.body]
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp ult i64 %i.0, 1000
+  br i1 %cmp, label %for.body, label %end
+
+end:
+  ret double %f_prod.0
+
+for.body:
+  %arrayidx = getelementptr inbounds [1000 x double], ptr %arr_d, i64 0, i64 %i.0
+  %0 = load double, ptr %arrayidx, align 8
+  %mul = fmul ninf double %f_prod.0, %0
+  %inc = add i64 %i.0, 1
+  br label %for.cond
+
+}
+
+define double @test_phi_nsz_flag_enabled() {
+entry:
+  %arr_d = alloca [1000 x double], align 8
+  br label %for.cond
+
+; CHECK-LABEL: for.cond:
+; CHECK: [[PHI_7:%.*]] = phi double [ 0.000000e+00, [[ENTRY_7:%.*]] ], [ [[MUL_4:%.*]] [[LOOPBODY_7:%.*]] ]
+; CHECK-NEXT: [[PHI_8:%.*]] = phi i64 [ 0, [[ENTRY_8:%.*]] ], [ [[INC_4:%.*]] [[LOOPBODY_8:%.*]] ]
+for.cond:
+  %f_prod.0 = phi double [0.000000e+00, %entry], [%mul, %for.body]
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp ult i64 %i.0, 1000
+  br i1 %cmp, label %for.body, label %end
+
+end:
+  ret double %f_prod.0
+
+for.body:
+  %arrayidx = getelementptr inbounds [1000 x double], ptr %arr_d, i64 0, i64 %i.0
+  %0 = load double, ptr %arrayidx, align 8
+  %mul = fmul ninf double %f_prod.0, %0
+  %inc = add i64 %i.0, 1
+  br label %for.cond
+
+}
+
+define double @test_phi_initalise_to_non_zero() {
+entry:
+  %arr_d = alloca [1000 x double], align 8
+  br label %for.cond
+
+; CHECK-LABEL: for.cond:
+; CHECK-NEXT: [[PHI_9:%.*]] = phi double [ 1.000000e+00, [[ENTRY_9:%.*]] ], [ [[MUL_5:%.*]] [[LOOPBODY_9:%.*]] ]
+; CHECK-NEXT: [[PHI_10:%.*]] = phi i64 [ 0, [[ENTRY_10:%.*]] ], [ [[INC_5:%.*]] [[LOOPBODY_10:%.*]] ]
+for.cond:
+  %f_prod.0 = phi double [1.000000e+00, %entry], [%mul, %for.body]
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp ult i64 %i.0, 1000
+  br i1 %cmp, label %for.body, label %end
+
+end:
+  ret double %f_prod.0
+
+for.body:
+  %arrayidx = getelementptr inbounds [1000 x double], ptr %arr_d, i64 0, i64 %i.0
+  %0 = load double, ptr %arrayidx, align 8
+  %mul = fmul fast double %f_prod.0, %0
+  %inc = add i64 %i.0, 1
+  br label %for.cond
+
+}
\ No newline at end of file